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Us a8a Don tawet r oulture
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U. S. DEPARTMENT OF AGRICULTURE.
OeFIGE OF EXPERIMENT STATIONS- BULLETIN NO. 121.
A. C. TRUE. Director.
THE METABOLISM OF NITROGEN, SULPHUR, AND
PHOSPHORUS IN THE HUMAN
H. C. SHERMAN, Pm. D.,
Instructor in J nalyfical Chemis'try!, Columbia University.
CONDUCTED IN COOPERATION
WITH COLUMBIA UNIVERSITY.
GOVERNMENT PRINTING OFFICE.
.!.... L......... .....
A. C. TRUE, Ph. D., Director.
E. W. ALLEN, Ph. D., Assistant Director and Editor of Experiment Station Record.
C. F. LANGWORTHY, Ph. D., Editor and Expert on Foods and Animal Production.
W. O. ATWATER, Ph. D., Chief of Nutrition Investigations, Middletown, C~on.
C. D. WOODs, B. S., Special Agent at Orono, 3e.
F. G. BENEDICT, Ph. D., Physiological Chemist, Middletown, Conii.
R. D. MILNER, Ph. B., Edidorial Assistant, Middletown, Conn.
A R .. R
NUTRITION INVESTIGATIONS. il
. D. WOODS, B. S., Special Aget at Orono, Ae.iil
A.~~~~~~~ ~ C.TUP.|. ieto.:i::
LETTER OF TRANSMITTAL.
U. S. DEPARTMENT OF AGRICULTURE,
OFFICE OF EXPERIMENT STATIONS,
Washington, D. C., October 1, 1902.
SIR: I have the honor to transmit herewith a report on experiments
on the metabolism of nitrogen, sulphur, and phosphorus in the human
organism, carried on by H. C. Sherman, Ph. D., instructor in analyt-
ical chemistry at Columbia University, New York, in cooperation with
this Department. The investigations were conducted under the imme-
Sdiate supervision of Prof. W. O. Atwater, chief of nutrition investi-
gations, and form a part of the investigations on the food of man
conducted under the auspices of this Office. Doctor Sherman's
investigations have for their special object a study of the cleavage of
protein, with reference particularly to the way in which this nutrient
serves for building tissue and as a source of energy. The results
given herewith constitute a progress report.
The report is submitted with' the recommendation that it be pub-
lished as Bulletin No. 121 of this Office.
Respectfully, A. C. TRUE,
Hon. JAMES WILSON,
Secretary of Agriculture.
Introduction-------- ------------------------------------------- 7
Metabolism and elimination of sulphur .....--------------....--...... 7
Metabolism and elimination of phosphorus --------.------------------ 10
Previous work on the comparative metabolism of nitrogen, sulphur,
and phosphorus -------------------------------------------- 13
Purpose and plan of the experiments --------- ---------------- 15
Analytical methods ---------------------- ---------------- --- 16
Composition of food materials ........................----------------------------- ..-----.. 18
Composition of feces-- .. ----------------- ---------------------- 19
Experiments on the digestibility of bread and milk -..--.--------------. 19
General description of experiments .- .------------------------- 19
Digestion experiment No. 1 .....------ .....---------...---. -------- 21
Digestion experiment No. 2 .. --------------.---------------- 22
Digestion experiment No. 3 -..------ ..-------------------. ---------- 23
Digestion experiment No. 4 .. ....... -------------------------- 23
...sition e feren--o.5------------------19
Digestion experiment No. 5 ........--------------..-----..------- 24
Digestion experiment No. 6 ---- ... .. ..---------------..---------- 25
Digestion experiment No. 7 ----. ----------------. ..--. ------ 25
Digestion experiment No. 8 -- ---- ----------- --------------- 26
Digestion experiment No. 9 ....---------.---- .--- ....----------------- 27
Digestion experiment No. 10 .. .. ... .... ... .. ...... 27
Results of digestion experiments ---- --------------------------- 28
Comparison of the metabolism of nitrogen, sulphur, and phosphorus ...... 31
Influence of loss of sleep .. -------...----------------------. 34
Lag of elimination after change of diet .----.----------. ----------- 36
Comparison of balance of income and outgo -.------------..---------. 43
Summary .................................--------------------..-------- 47
*L:r :::". -
FIG. 1. Diagram showing the fluctuations in the daily excretion of nitrogen
and phosphorus during the first series of experiments (Nos. 1-3)-
2. Diagram showing fluctuations in the daily excretion of nitrogen
and phosphorus during the second series of experiments (Nos. 4
and 5) -- --- --------. --- -----------
3. Diagram showing fluctuations in the daily excretion of nitrogen,
sulphur, and phosphorus during the third series of experiments
(Nos. 7-10) ......................... ................-
METABOLISM OF NITROGEN, SULPIIUR, AND PHOSPHORUS IN
TIHE IIIMAN ORGANISM.
Most of the digestion experiments heretofore reported in connection
with the nutrition investigations of this Department have included
the determination of the balance of income and outgo of nitrogen,
while in those carried out in the respiration calorimeter the balance
of carbon, hydrogen, and energy are likewise determined. It is
believed that in many cases the determination of income and outgo
of sulphur and phosphorus will add considerably to the interest and
value of these investigations.
The sulphur or phosphorus balance, like the nitrogen balance, -may
be found by comparing the amounts ingested in the food with those
eliminated through the kidneys and intestines. So far as is known
no phosphorus and only traces of sulphur escape in the form of vola-
tile compounds, and the quantities of sulphates and phosphates in the
perspiration are so small that they may probably be neglected, unless
in exceptional cases.
METABOLISM AND ELIMINATION OF SULPHUR.
Small quantities of sulphates occur in foods and in some waters.
'By far the greater part of the sulphur of the food enters the body in
organic combination, in proteids or albuminoids. When proteid t l,
matter is oxidized in the body most of the sulphur is burned to sul-
phuric acid, the greater part of which appears in the urine as normal
inorganic sulphates. A smaller part of the sulphuric acid (in health
usually about one-tenth) is found in the form of ethereal sulphates,
i. e., combined with organic radicles, the latter being usually regarded
as derived chiefly from intestinal putrefaction of proteids. Such
putrefaction may give rise to the formation of hydrogen sulphid, which
may either appear as sulphids, chiefly of iron and the alkali metals,
in the feces, or may be absorbed into the system, or may to some
extent escape with the intestinal gases. The total sulphates of the
urine may readily be determined by precipitation as barium sulphate
after boiling the urine with hydrochloric acid to set free the sulphuric
acid in "ethereal" combination. Not all of the urinary sulphur,
however, exists in the form of sulphates. About 15 to 20 per cent is
8 -::.. :: --
usually found in less completely oxidized forms, this portion being:
called "unoxidized or "neutral" sulphur, to distinguish it from the
fully oxidized sulphate-sulphur. The existence of sulphur in other
forms than sulphates in the urine was discovered by Ronalds at. ,
Giessen in 1846,a but was first brought into prominence by Bischof
and Voit in 1860.b Several compounds have been described as edn-
tributing to the "neutral" sulphur of the urine. The taurin of the"
bile is held to be largely reabsorbed from the intestines and eliminated
through the kidneys. If taurin be fed directly the amount of neutral
sulphur in the urine increases, according to Salkowski,e and in experi-
ments upon a dog with a biliary fistula the neutral sulphur was found
to decrease, but did not entirely disappear.' Among other sulphur
compounds which have been found in the urine may be mentioned sul-
phocyanids, originally derived from swallowed saliva," thiosulnhate:
small quantities of cystin, of mucinand occasionally of hydrogen
sulphid. Abel g has described a body which yields ethyl sulphid, and
it is probable that other compounds remain to be discovered, since the
quantities of the above compounds believed to exist in normal urine
are not sufficient to account for all of the neutral sulphur found.
According to Spiegel the appearance of cystin and hyposulphites
in the urine points to a condition of diminished oxidation, since these
compounds though constantly formed in the body are not normally
end products of metabolism.
The following quotations from recent text-books (which are-given in A
chronological order) are believed to fairly represent the present general
teachings in regard to the significance of the sulphur metabolism and
its relation to the metabolism of nitrogen.
Halliburton i says:
The sulphuric acid of the urine is in part combined as ordinary sulphates, in
part as ethereal sulphates. It is derived to a small extent from the food, int
chiefly from the metabolism of proteids, the amounts of sulphuric acid and ure ;i
in the urine running parallel.
According to Hammarsten:J
The sulphuric acid of the urine originates only to a very small extent from the -
sulphates of the food. A disproportionally greater part is formed by the burning
a Falck's Beitrage zur Physiologie, Hygiene, etc., p. 102.
bGesetze der Ernahrung des Fleischfressers, pp. 279-284, 302-303.. "
ScCf. Lusk, American Text-book of Physiology, Vol. I, p. 507. -
dKunkel, Arch. Physiol. [Pfliger]. 14 (1887), p. 353.
eLeared, Proc. Royal Soc. London, 1870. pp. 16,18; I. Munk, Arch. Path. Anat. :
Physiol. [Virchow], 69 (1877). p. 354.
f Goldmann and.Baumann, Ztschr. Physiol. Chem., 12 (1888), p. 254.
9 Ztchr. Physiol. Chem 20 (1894). p. 253.
SArch. Path. Anat. u. Physiol. [Virchew], 166 (1901), pp. 364-371; abs. in
Jour. Chem. Soc. [London], 82 (1902), No. 471, II. p.93. -
li Schaffer's Text-book of Physiology, Vol. I, 1898, p. 79.
4 S Text-book of Physiological Chemistry, trans. by J. A. Mandel, 1898, p. 15.
.. ..:..i '-m.!
of the proteids containing sulphur within the body, and it is chiefly this forma-
tion of sulphuric acid from the proteids which gives rise to the previously men-
tioned excess of acids over the bases in the urine. The quantity of sulphuric acid
eliminated by the urine amounts to 2.5 grams H2SO, per 24 hours. As the sul-
phuric acid chiefly originates from the proteids, it follows that the elimination of
sulphuric acid and the elimination of nitrogen are nearly parallel, and the rela-
tionshi N : HSO, is about 4-5 A complete parallelism can hardly be expected,
as in the t place, a part of the sulphur is always eliminated as neutral sulphur,
and secondly, because the low quantity of sulphur in different protein bodies
undergoes greater variation as compared with the high quantity of nitrogen con-
tained therein. Generally the relationship between the elimination of nitrogen
and sulphuric acid under normal and diseased conditions runs rather parallel.
In Novy's a opinion:
The proteins of the food and of the tissues constitute almost the sole source of
the sulphur containing waste products. A small amount of waste sulphur com-
pounds is eliminated as sulphocyanate by the saliva, gastric juice, etc. Another
small portion leaves the body as taurin in the taurocholic acid of the bile. With
these exceptions almost all the sulphur resulting from protein disintegration
appears in the urine. Inasmuch as the sulphates contain most of the waste sul-
phur it follows that the total sulphates in the urine furnish an excellent index of
According to Ogden :
The total quantity of sulphuric acid in the twenty-four hours' amount of urine
of an adult taking a mixed diet is from 1i to 3 grams, or an average of 2 grams.
About one-tenth of the total sulphuric acid is in the form of ethereal sulphates.
In general it may be stated that the variation in the quantity of ordinary sulphates
eliminated in the urine runs parallel to that of urea.
Lusk. states that:
Sulphur is built in the proteid molecule of the plant from the sulphates taken
from the ground. It is found in albuminoids, especially in keratin. As taurin
it occurs in muscle and in bile, as iron and alkaline sulphids in the feces, as sul-
phureted hydrogen in the intestinal gas, as sulphate and other unknown com-
pounds in the urine. The total amount of sulphur in the urine runs o _,
Proportionately parallel with the amount of nitrogen; that is to say, the amount I, ,
is proportional to the amount of proteid destroyed. When an animal
eats proteid and neither gains nor loses the same in his body, the amount of sul-
phur is equal to the sum of that found in the urine and feces. Sulphates eaten
pass out through the urine. They play no part in the life of the cell.
Thus there is general agreement in regarding the sulphur of the
urine as essentially derived from katabolism of proteid in the body,
so that the quantity eliminated is, like that of nitrogen, an indication
of the amount of proteid matter broken down. This agreement in
regard to the parallelism of the nitrogen and sulphur excretion is,
however, by no means exact, since in some cases the reference is to
total sulphur, in others to total sulphates, and in still others to ordi-
aPhysiological Chemistry, second ed., 1898, pp. 194, 195.
bClinical Examination of the Urine, 1900, p. 111.
SAmerican Text-book of Physiology, second ed., Vol. I, 1900, pp. 505, 507.
Of the authors quoted, Hammarsten is the only one to call atten-
tion to the fact that this parallelism will be affected by the variations
in the relative proportions of nitrogen and sulphur in different pro-
teids. That these variations are very large will be seen from a cor- <
prison of the accepted analyses of a few representative proteids.
Taking, for instance, the elementary analyses recently compiled by >
Osborne in connection with his discussion of the sulphur in proteid
bodies,a we estimate from the percentages given that the ratio of I
nitrogen to sulphur is, in legnin as 46.9: 1; in 26.9: 1; ii edegtin,
21.2:1; in bynin, 19.4:1; in liadin, 17.2:1; and in leucosin, 13.1:1
From this it will appear that the typical proteids of wheat furnish
about three times as much sulphur, with a given amount of nitrogen,
as the typical proteid of the legumes. The ratio in casein (19.7:1) is
about twice as great as in egg albumin (9.6:1). Among the proteid ',,
constituents of the body the differences are even greater than among i
the food proteids just mentioned. In oxyhaemoglobin the ratio is .
44.6:1; in mosin, 13.1:1; in serum globuiu, 14.3:1; in fibrinogen, ,
13.3:1; in serum albumin from human exudation, 7.06:1; in chon-
dromucoid b 5.2:1; in tendon-mucin,b 5:1, and in osseomucoidlb 5:1.
Thus it would appear that the katabolism of sufficient glucoproteid
to yield a gram of nitrogen would result in the elimination of about
three times as much sulphur as the katabolism of an equivalent
amount of myosin, serum globulin, or gliadin, and nearly ten times i
as much as would come from an equivalent amount of oxyhsemoglo-
bin or of legumin. It is evident, therefore, that the ratio of nitrogen
to sulphur in the urine may undergo considerable variation as the
result of changes in the kind of proteid given in the food or in the
kind of body tissue katabolized in case the protein of the food is
insufficient. The interesting investigations of Kolpateka noted belo
(p. 13) are based largely on these variations. There is, however
every reason to believe that so long as the diet is uniform, and other :
conditions normal, the metabolism and elimination of sulphur wi
be nearly parallel with that of nitrogen; and this seems to be true no
only as concerns the twenty-four hours' urine, but usually for shor
periods as well. (See p. 45.)
METABOLISM AND ELIMINATION OF PHOSPHORUS.
Phosphorus enters the body in organic combination in the form of
nucleins, nucleo-proteids, lecithin, protagon, and perhaps glycerol-
aConnecticut State Sta. Rpt. 1900, p. 464; Jour. Amer. Chem. Soc., 24 (1902),
& The ratios given for the glucoproteids are from figures given by Hawk and
Gies (Amer. Jour. Physiol., 5 (1901), p. 416. In the case of osseomucoid the aver-
age of the later and purer preparations is taken. The figures for tendon-muciili
(Chittenden and Gies) have recently been confirmed by Cutter and Gies (Amer.
Jour. Physiol.. 6 (1902). p. 155. The figures for chondromucoid are from the work
of Morner (Ztschr. Physiol. Chem., 18 (1893), p. 213.
phosphoric acid, but a larger quantity is taken as mineral phosphates
in the food. The proportion of phosphorus eliminated by the intes-
tine depends mainly on the nature of the food and the alkalinity of
the blood. Herbivora excrete nearly all of the phosphorus with the
feces, and in man the amount thus excreted is greatest on a vegetable
diet or one rich in lima salts, and may be largely increased by feed-
ing alkaline citrate and calcium carbonate, the first to furnish the
more alkaline reaction to the blood and urine, the second to form with
the phosphoric acid the insoluble phosphate of lime (Lusk).a
f The phosphorus of the urine is present chiefly as phosphates of
the alkalies, with a much smaller quantity of phosphates of the
alkaline earths. A very small proportion is present in organic com-
bination. This has been believed to exist as glycerol-phosphoric
acid. Jolly,6 however, claims to have found in the urine certain
peculiar nitrogenous compounds, which retain some mineral phos-
phate in such intimate association that the phosphoric acid is not
precipitated by the usual reagents, and he believes that it is these
phosphates and not glycerol-phosphoric acid or any incompletely oxi-
dized form of phosphorus which escapes precipitation by the ordinary
Since the phosphorus of the urine comes so largely from the simple
passage through the system of the phosphates taken in the food, it
follows that variations in the quantity eliminated are more apt to
be connected with the diet than with the metabolism of body mate-
rial. The idea once held that the quantity of phosphorus eliminated
is principally dependent upon the metabolism of nervous tissue was
soon abandoned. In this connection Voitc stated that the bones
contain about 1,400 grams of phosphorus, the muscles about 130
grams, and the brain and nervous system about 12 grams. Moreover,
by comparing the loss of weight of different organs in the starving
dog, with the changes in the ratio of nitrogen to phosphorus in the
urine, he was able to show that the body material katabolized was
largely contributed by the bones.
Recent work tends to emphasize the importance of the nucleins and
related bodies and to confirm the view that the phosphates found in
all the organs and tissues of the body are to a considerable extent in
chemical combination with the proteid matter. Thus it is stated that
when the body stores proteid a proportionate amount of phosphoric
acid is retained for the new protoplasm, while on destruction of pro-
teid the phosphoric acid corresponding to it is eliminated.d
aSee also the recent work of Paton and his associates (Jour. Physiol., 25 (1900),
p. 212), comparing the metabolism and elimination of phosphorus in the dog and
in the goat.
bCompt. Rend. Acad. Sci. Paris, 127 (1898), 118.
c Hermann's Handbuchdes Physiologie, vol. 6, pt. 1, p. 80.
d Lusk, American Text-book of Physiology, second ed., 1900, Vol. I, p. 575.
The significance of the phosphorus metabolism from the medical|
standpoint is quite fully discussed by Bergell.a I1
Several investigators" have recently studied the urinary exeret~ion
of phosphates as influenced by those conditions which are believed to
be especially connected with the metabolism of nucleins.
An intimate connection between changes in the phosphorus eliai- .
nated and in the katabolism of nucleins is evidently assumed-by :
Dunlop, Paton, Stockmann, and Maccadam in interpreting the results
of their investigations of the effects of muscular exertion. In them
experiments each subject maintained a uniform diet for seven days,:
on the fourth of which as much exercise (bicycle riding) was taken as !*
the subject could endure without serious discomfort. In each ease
the day or days following the exertion showed an increased elimina- i
tion of nitrogen and sulphur, but only when the subject was in poor
training was there a corresponding increase in the elimination of .
phosphates and of uric acid. From this it was concluded that with :
the subject in good training only muscle proteid is broken down, ,.;||
while if the subject be in poor training this consumption of muscle :
proteid is accompanied by the consumption of the material of other
tissues which contain nucleo-proteid. In this connection it is inter- ".HI
testing to note the observation previously made by Preysz," that the
increased elimination of phosphoric acid resulting from walking given
distance (25 kilometers) was considerably greater when the distance i:
was walked at a rapid rate, causing a more intense though less pro- '
As already stated, the greater part of he phosphorus eliminated
comes from the phosphates of the food. iWhen, however, the diet is
uniform, a variation in the phosphorus elimination must be taken as :;:
showing some change either in body metabolism or in the condition of
the body with reference to its store of phosphates. Whether or not .
the connection between urinary phosphates and the katabolism of :
nucleins is as intimate as some investigators seem to assume, it is evi-
dent that the study of the phosphorus balance may give valuable
information which could not otherwise be obtained regarding the1
nature of the changes taking place in the body.
a Fortschr. Med., 16 (1898), p. 1. Bedeutung der Phosphorsaure in mensec-
lichen und thierschen Organismen. Inaug. Diss., Berlin, 1898.
bMoraczewski, Arch. Path. Anat. n. Physiol. [Virchow], 151 (1898), p. -2; 21i
Milroy and Malcolm, Jour. Physiol., 23 (1898), p. 217, and 25 (1899), p. 105; White
and Hopkins, Ibid., 24 (1899), p. 42; Loewi, Ar h. Exper. Path. u. Pharmakol., 44
(1900-1901), p. 1; abs. in Jour. Chem. Soc. [London], 78, 1900, II, p. 417.
SJour. Physiol., 22 (1897-98), p. 68.
d Ungar. Arch. Med., 1 (1892-93), p. 38; reviewed in Arch. Physiol. [Pflfger],
54 (1893), p. 21.
PREVIOUS WORb ON THE COMPARATIVE METABOLISM OF
NITROGEN, SULPHUR, AND PHOSPHORUS.
The course of the elimination during the day.-Considerable atten-
tion has been given by different investigators to the course of the
elimination of nitrogen and of phosphorus during the day. The
recent work of Rosemanna on nitrogen and of his pupil Roeske6 on
phosphorus may be especially noted. Unfortunately such studies
have usually been made upon only one element at a time. In some
recent experiments carried out in the laboratories of Wesleyan Univer-
sitye the course of elimination of nitrogen, sulphur, and phosphorus
has been observed simultaneously, the urine being collected in the
three-hour periods during the day with one nine-hour period at night.
The rates of elimination of nitrogen and sulphur were found to run
nearly parallel, rising and falling twice during the day and reaching
a minimum during the night. The fluctuations, though quite reg-
ular, were not very great, the highest rate of elimination found dur-
ing the day being usually about one-fourth greater than the average
rate for'the nine hours of the night. The elimination of phosphorus,
on the other hand, did not run parallel with that of nitrogen and
sulphur, and the fluctuations, though less regular, were considerably
larger, the maximum rate of elimination being two to three times as
great as the minimum. Moreover, the minimum rate of elimination
of phosphorus was reached not during the night, but at some time in
the forenoon, usually from one to three hours, but sometimes from
four to six hours after rising.
Comparative metabolism during periods of a day or more.-Many
metabolism experiments have been made in which nitrogen and phos-
phorus were determined and a smaller number in which sulphur was
also included. Several of these investigations will be referred to later
in connection with the discussion of the results of experiments here
reported. 'The investigations of Kolpatckad are, however, so sugges-
tive that they should be mentioned here. The subjects were in all cases
dogs, and the object of the work was to learn the real source of the
nitrogen in the urine-to determine whether it is derived directly from
the protein of the food, from protein stored in the body, or from actual
proteid tissue-and further, to study the nature'of the stored protein.
aArch. Physiol. [Pfliiger], 66 (1896), p. 343.
b Ueber den Verlauf der Phosphorsdure Ausscheidung beim Menschen. Inaug.
Dies., Greifswald, 1897.
cSherman and Hawk, Amer. Jour. Physiol., 4 (1900), p 25, and unpublished
results by Atwater and Hawk and by Hawk and Chamberlain. These experi-
ments are more fully described in connection with the discussion of "lag" on
dPhiziologicheskii Sbornik. A. I. and V. I. Danilevski, editors. Kharkov,
1888, Vol. I, p. 53; abs. in U. S. Dept. Agr., Office of Experiment Stations Bul. 45,
p. 308, a2.
Kolpatcka endeavored to solve these problems by comparing the
ratios of phosphoric acid to nitrogen and of sulphur to nitrogen in
the food consumed and in the urine. The ratios found in the foods
used were as follows: In meat, POs:N::1:7.3; S:N::1:15.6. In
gelatin, which contains no P2Os, the ratio is as follows: S: N:: 1: 22.5.
In whites of eggs, P2O:N:: 1: 46; S:N::1:9.8. In yolks of eggs,
P205:N::1:1.8. Knowing the ratios of these elements in the food T
and in the urine during partial or complete fasting, it was held to be '
possible to judge whether the nitrogen in the urine for any particular
period came from the food consumed, from stored protein, or from
actual body tissue. Thus on a meat diet the ratio of PO,:N in the
urine was nearly the same as in the food, and ikt was concluded that
the excreted nitrogen came directly from the food. During a period
of fasting following the meat diet the relative proportion of phosphorus
excreted gradually increased until the fifth day, after which the ratio
was nearly constant, PO,: N:: 1: 4 (about). A similar change in the
ratio was found after a change from meat diet to a diet of fat and
starch. These results are held to show that when the supply of pro-
tein is cut off there follows a katabolism, first of protein simply
stored from the previous diet and not yet organized, then of protein .
from body tissue, this last being the sole source after the fifth day
and yielding a relatively large proportion of phosphorus. The
increased proportion of "earthy" phosphates led to the belief that
some of the "tissue protein" came from the bones, a conclusion
reached several years ago by Voit. (See p. 11.)
On passing from a meat ration to a ration of white of egg there was
a diminution of phosphoric acid and an increase of sulphur. The
ratios, however, varied considerably, and a relatively large amount of
phosphoric acid in the first days was attributed to a destruction of
some body protein. In passing from a meat to a gelatin ration the
amount of nitrogen in the urine increased, while the amount of phos-
phoric acid decreased but did not entirely disappear, thus giving
additional evidence that gelatin alone can not prevent the breaking
down of protein tissue. In several cases the experiments were
repeated with substantially the same result. So far as can be judged
from the available data of these experiments, some factors seem to
have been overlooked by Kolpatcka which would affect the interpre-
tation of the results. Among these is the "lag" in the excretion of
the products of metabolism, which would have an important influence
upon the changes in the urine following a change in the ration, or *
during the first days of fasting. Moreover, the lag may be different
for the three elements under discussion, and these differences may be
influenced by the nature of the diet. The amounts of nitrogen, sul-
phur, and phosphorus in the feces are recorded but do not seem to
have been included in determining the ratios. These quantities were
generally not large, but in several eases the phosphorus of the feceis.
: 7*:5 il
was over 10 per cent of the total excretion. The phosphoric acid
determinations were in all cases made by titration with uranium ace-
tate. For urine this may be considered fairly satisfactory; with meat
and other materials containing appreciable amounts of iron the errors
might be larger. Thus this investigation, whild of great value and
certainly rich in interest and suggestion, seems to neglect some fac-
tors which are still in need of investigation and which may appreci-
ably affect the interpretation of the results obtained. These factors
would be of even greater importance in experiments upon the human
subject, where either the balance of income and outgo or the "lag,"
or both, may be more or less influenced by the mental and nervous
condition, and where often a much larger proportion of the phosphorus
leaves the body through the feces. If this fecal phosphate is an indi-
gestible residue it should be deducted from the amount in the food
before calculating the ratios discussed above. If, on the other hand,
it has been metabolized and excreted into the intestine, it should be
added to the amount eliminated in the urine. Much work is being
done in the attempt to distinguish between the nitrogen of undigested
residues and that of metabolic products. In the case of phosphorus
this distinction is of greater relative importance, because the per-
centage of the ingested phosphorus eliminated in the feces is apt to
be much larger than that of the ingested nitrogen.
PURPOSE AND PLAN OF THE EXPERIMENTS.
The work here reported comprises 10 experiments with man on a
milk and bread diet, in each of which the digestibility of the nutrients
of the food and the income and outgo of nitrogen, sulphur, and phos-
phorus were determined. In most cases two or more experiments
were arranged in series, so that the change in diet gave an opportunity
to determine whether the alteration in the excretion occurred simul-
taneously for the three elements studied; in other words, to compare
the "lag" of sulphur and of phosphorus with that of nitrogen. The
general purpose of the study was thus twofold-to accumulate addi-
tional determinations of the digestibility of bread and milk diet, and
by collecting data regarding the comparative metabolism of nitrogen,
sulphur, and phosphorus to prepare the way for the study of the latter
elements in connection with certain of the nutrition investigations
carried on by the Department of Agriculture. Attention has there-
fore been mainly directed to points which of themselves might not be
of much interest, but which are likely to influence the methods of
experimenting or the interpretation of the results. Among these
points may be mentioned the question of "lag" already referred to,
the influence of a change of routine, such as marked loss of sleep, the
gain or loss of sulphur and phosphorus while the body is gaining or
losing nitrogen, the proportion of urinary sulphur in forms other than
sulphates and of phosphorus in forms other than phosphates, and the
question whether the large proportion of phosphorus which leaves 1:"thebs
body by the feces is incapable of absorption, or is not absorbed because
not needed, or has been metabolized in the body and excreted through
For convenience of reference the digestibilities of the nutrients i ji
the different experiments are first reported in the form which has:
been followed in previous bulletins of this series, after which the
metabolism of nitrogen, sulphur, and phosphorus is discussed in a
All food materials used in the investigation were sampled at the
time of use and all the feces were collected, dried, and analyzed.
The methods of analysis were mainly those of the Association of Off-
cial Agricultural Chemists." The determination of ether extract in
the feces gave in some cases variable results and is not considered
entirely satisfactory. The bread (soda crackers) and butter used in
the experiments were generally prepared in advance in sufficient quan-
tity for several experiments, thus reducing the number of analyses
required. The milk used was obtained by mixing the entire product
of a small local herd and was delivered in bottles. Previous experi-
ence had shown that the milk obtained from this source was almost
uniform from day to day. In the present experiments a composite
sample was prepared for each experimental period by taking a pro-
portionate amount of the milk at the time of weighing the portion for
each meal. In the fresh sample for. each period the nitrogen and
either the fat or the total solids was determined, after which a portion
was dried, ground, and submitted to complete analysis. In case the ::
partial analyses of samples of milk used in successive experiments of
a continuous series showed no greater differences than occur in dupli-..
cate determinations on a single sample, the dried residues were ground
together into a single composite sample for complete analysis.
Heat of combustion was determined by means of the Atwater-
Blakeslee bomb calorimeter, as described in previous publications,
urine being previously dried on blocks of cellulose in the usual-
Sulphur in foods and feces was oxidized to sulphuric acid, some- :
times by fusion with sodium hydroxid and potassium nitrate in the
usual manner and sometimes by burning the material in the bomb
calorimeter. The latter method is quicker and more convenient in
every way and, so far as we have employed it, gives the same results
as the alkaline fusion method. The method of oxidation in the bomb
a U. S. Dept. Agr., Division of Chemistry Bul. 46.
bIT. S. Dept. Agr., Office of Experiment Stations Bul. 21, p. 120; Connecticut .
Storrs Sta. Rpt. 1897, p. 199."
cLandw. Vers. Stat., 47 (1896), p. 297; U. S. Dept. Agr., Office of Experimet.
Stations Bul. 69, p. 23.
wr rrr, "~~c
as here used was practically an adaptation of that given by Hempel.a
The substance was pressed into a pellet and burned in the same
manner as in determining the heat of combustion; then by means of
a special coupling the gas in the bomb was allowed to escape slowly
through an outlet tube having very narrow bore and was passed
through bromin water in a U-tube containing glass beads. The
moisture condensed on the cover and lining of the bomb was thor-
oughly washed out and united with the bromin water and rinsings
from the U-tube, more bromin water added, if necessary, and the
solution boiled to insure the oxidation to sulphuric acid of any sul-
phurous acid which may have been formed. The platinum capsule
jn which the pellet was burned was placed in a small beaker and
heated with hydrochloric acid, to dissolve any sulphates in the ash.6
This solution was then added to the one just mentioned and the whole
filtered and precipitated with barium chlorid in the usual manner.
As the solution always contained some iron from the igniting wire
and the precipitates of barium sulphate were small and formed slowly,
the latter were allowed to stand overnight in the cold before filter-
ing. In the work here reported this method was used only to check
some of the results obtained by the fusion method, but it has since
been studied in some detail (see below).
In oxidizing the sulphur of foods and feces by the usual fusion
S method, from 1 to 3 grams of sample was melted with 7 to 12 grams
of sodium hydroxid containing a little potassium nitrate; afterwards
more nitrate was added in small portions until the oxidation was
complete. The fusions were made in silver vessels heated by alcohol
lamps. The fused mass after cooling was dissolved in water and
twice evaporated to dryness with excess of hydrochloric acid, after
which it was taken up with acidulated water and precipitated in the
usual way. In estimating the total sulphur in urine, 40 cubic centi-
meters were evaporated to dryness in a silver dish or crucible and
the residue treated as just described. The amount of sulphur intro-
duced by the reagents used was determined and the corresponding
corrections applied to the results obtained.
For the determination of phosphorus the material was oxidized either
by means of caustic soda and potassium nitrate in the same manner
as for the determination of sulphur, or by fusion with sodium carbon-
ate and potassium nitrate in a similar manner. In the latter case the
fusion was made in a platinum dish over a Bunsen burner. In either
case the fused mass after cooling was dissolved in water, treated with
aBer. Deut. Chem. Gesell., 30 (1897), p. 202.
bin the presence of barium sulphate it would, of course, be necessary to fuse
this residue. In the ordinary foods it seems safe to assume the absence of appre-
ciable quantities of barium.
9861-No. 121-02-- 2
nitric acid in considerable excess, and the solution boiled down to
small bulk, after which it was diluted, filtered if necessary, and the
phosphoric acid determined by the molybdate-magnesia method, fol-'; V
lowing the details adopted by the Association of Official Agricultuira.
Chemists and using special care to insure' the purity of the final
The study of methods for the determination of sulphur and phos-
phorus has been continued since the completion of the experiments
described in the bulletin. A comparison of the method of fusion with
alkali and an oxidizing agent with that of combustion in oxjrgen
showed practically identical results in the determination of sulphur
and confirmed our preference for the latter method.
In the determination of phosphorus practically the same results.:,
were obtained whether the material was oxidized by means of carbon-
ate and nitrate as above described, by combustion in oxygen as in
the determination of sulphur, or by boiling with sulphuric acid and
The details of this study of methods have been published else-
COMPOSITION OF FOOD MATERIALS.
The milk used has already been described. For bread the material
selected was commercial "soda crackers" or "soda biscuit," these Z
being readily obtainable of practically uniform composition and easily ":ll
kept without undergoing change or becoming distasteful. The butter
was an ordinary product of good quality. The analyses of the food
materials are given in Table 1.
TABLE 1.-Composition of food materials.
ratory Pro Car- En- Phoa
r Material. Water. no tein N Fat. boy- Ash. ergy Sn
shofegen. pr al irate per phnr. Plhr .:Ie
x 6.25). pertph
650 Crackers (ex peri- Per ct. Per ct. Per ct. Cals. Per ct. Per ct.--
ments Nos.1-5) ..- 9.32 1.610 10.06 6.21 72.32 i 2.09 4.221 0.10 0 ..
651 Milk (experiments 4.98' .6 .0 es
I Nos.1-3) ----.--- 86.51 .535 3.3 4.42 4.98 5 767 .
652 Milk (experiments
Nos.4-5)-----------.86.74 .542 3.391 4.26 4.86, .75 .778 .042 .0
653 Butter (experiments
Nos.1-4) ............ 9.11 .180 1.13 86.97 -------- 2.79 8.010 ................
654 Milk (experiment I i I
No.6).---. -------- 87.08 .495 3.09 4.26 1 4.90 .67 .780 .084 .0
655 Crackers (experi-
ment No.6)......... 10.21 1.820 11.38 6.18 70.39 1.84 4.172 .143 .115
656 Crackers (experi-
ments Nos.7-10)... 7.31 1.680 10.50 6.49 73.38 2.32 4.301 .130 .100
657 Milk (experiments
Nos.7-9)....----------- 86.73 .506 3.16 4.57 4.81 .73 .795 .081 .004
658 Milk (experiment I
No.10) ---.....- 86.50 .522 3.2 4.53 5.01 .70 .780 .008 .
a Jour. Amer. Chem. Soc., 24 (1902), p. 1100.
COMPOSITION OF FECES.
As stated above, the feces were analyzed by the same methods as
the food materials. The composition of the feces from the various
experiments here.reported is shown in Table 2, the results being given
on the water-free basis, since the amount of water in the fresh feces
has no bearing on the questions here studied.
TABLE 2.-Composition of feces.
>Q.. r.- X a .U
+21 ; ;|
..Feces. ce- ,ol
0 'C -4 .
0 PS.B a c (" Sa
Id 84 4 3 C t
Per Per Per Per Per Per Calo- Per Per
SGmns. Gms. cent. cent. cent. cent. cent. cent. ries. cent. cent.
.. 0 Experiment No. 1..... 4 97.5 95.1 97.51 3.12 19.50 13.63 38.28 28.59 5. 686 0.268 3.26
661 Experiment No. 2.--- 4 102.1 99.1 97.09 2.72 17.00 16.69 36.70 29.61 5.696 .246 2.96
: 8 Experiment No. 3... 4 99. 4 95.0 95.57 2.93 18.311 16.01 35.92 29.76 5.466 .272 3.26
.s Experiment No. 4.... 3 73. 5 70.4 95.74 4.19 26.19 21.37 :0. 46 21.98 6.043 385 1.86
.6 Experiment No. 5--..- 4 128.0 123.5 96.48 2.82 17.63. 9.78 38.91 33.68 5.145 .270 3.56
065 Experiment No. 6---.... 4 39.0 37.2 95.29 2.84 17.75 10.75 40.08 31.42 5.514 .246 3.97
l Experiment No. 7....5 80.0 77.0 96.32 2.94 18.38 12.24 39.67 29.71 5.574 253 3.88
077 Experiment No. 8---- 5 200.0 188.6 94.29 2.75 17.18 16.94 36.36 29.52 5.782 229 3.77
68 Experiment No. 9.. 5 82.1 77.7 94.64 2.77 17.31 11.59 40.02 31.08 5.503 238 3.22
9 Experiment No. 10 ... 3 104.2 100.3 96.25 3.14 19.62 10.48 37.79 32.11 5.271 295 4.11
EXPERIMENTS ON THE DIGESTIBILITY OF BREAD AND MILK.
GENERAL DESCRIPTION OF EXPERIMENTS.
The experiments here reported were made during the years 1900 and
1901. The subject was a healthy young man (the writer) with good
appetite and apparently normal digestion and nutrition. The meals
were taken iii the laboratory, sometimes in the company of other
young men engaged in similar experiments and sometimes alone. In
each case (with a single unimportant exception, noted below) the diet
was decided upon in advance, and was maintained uniform through-
out the experiment or series of experiments. Exactly one- third of the
day's ration was taken at each meal, and the meals were taken at
nearly uniform hours: In the series of 1900, at 6.30 a. m., 12.30 p. m.,
and 6.30 p. m.; in that of 1901, at 7.30 a. m., 1 p. m. and 6.30 p. m.
Excepting the butter, which was prepared in advance in weighed por-
Stions, the food required for each meal was weighed by the subject
S.During the time covered by the experiments the subject was
. engaged partly in the analytical and other laboratory work connected
.. with .the investigation and partly in preparing for publication the
S results of previous studies. Little exercise was taken aside from that
involved in the laboratory work, which was somewhat exacting.
.. ...' ..' 4,
Several of the experiments were arranged in series, and followed
each other without intermission. In other cases the food taken on
the day preceding the beginning of the experiment was practically the
same as during the experimental period. Each experimental period
began with breakfast, and the lampblack used to facilitate the sepa- : 'I
ration of the feces was taken with this meal instead of with the pre-
ceding supper. In our experience it is very much easier to determine
the point which marks the first appearance of the feces from a meal
with which lampblack was taken than to decide exactly where the
feces from such a meal end; apparently because, as would be expected,
enough lampblack may sometimes adhere to the walls of the intestines
to give more or less color to the feces from meals subsequent to that
with which it was taken. It seems, therefore, decidedly preferable to
take the lampblack with the first meal of the period and the first meal
following the period, so that the point of separation shall be in each
case the point at which the lampblack first appears in the feces. In
each of the digestion experiments the urine was collected, beginning
with the time at which the first breakfast was taken, and the nitrogen,
sulphur, phosphorus, and heat of combustion determined.
The details of the digestion experiments are included in the follow- :::
ing tables. These show the kind and amount of food eaten by the
subject and the weight of the subject at the beginning and end of the
experiment. The amount of protein, fat, and carbohydrates in each
food material and in the feces was computed from the weight of each
material multiplied by its percentage composition as shown in Tables ..''
1 and 2. The heats of combustion, shown in the last column of the
tables, were determined by burning the material in the bomb calorim-
eter and multiplying the total weight of food or feces by the heat of
combustion of 1 gram, as thus determined. The differences between
the total nutrients in the food eaten and those rejected in the feces
are taken as a measure of the total amounts digested, although of
course the feces do not consist entirely of undigested residues, but
contain a relatively -large amount of metabolic products.a The
amounts of nutrients rejected in the feces, while not strictly repre-
senting the undigested portion of the food, do represent approximately
the amounts which are not available to the body. The total amount
of any particular kind of nutrient digested or available divided by the
total amount of this nutrient in the food gives the percentage which
is. digestible or actually available to the body. These percentage
values are called coefficients of digestibility or availability. i
While the coefficients of digestibility of the different nutrients rep-
resent the proportion which the body actually utilizes, the correspond-
ing value for the heat combustion of the food does not represent the
SSee discussion of this subject in Connecticut Storrs Sta. Rpts. 1896, p. 166, and
1897, p. 156.
. ::Iii ::"
Sa Urea contains 46.67 per cent nitrogen and has a heat of combustion of 2.54
calories per gram. One gram of protein (16 per cent nitrogen) would yield
(16-46.67=) 0.342 gram urea with a heat of combustion of (2.54x0.342=) 0.87.
See also U. S. Dept. Agr., Office of Experiment Stations Bul. 53, pp. 27 and 28.
.. ... ....
actual amount of energy which the body obtains from the food absorbed
from the alimentary canal. When protein is burned in the bomb
calorimeter, the carbon is oxidized to carbon dioxid and the hydrogen
to water, the nitrogen being reduced to the free state. When protein
is burned in the body, however, the oxidation is not so complete. The
nitrogen is excreted in the form of urea, uric acid, and other com-
pounds, which also contain small amounts of carbon and hydrogen,
together with some oxygen. In estimating the actual fuel values of
the digestible nutrients of the food, allowance must be made for these
incompletely oxidized residual products which are excreted by the
kidneys. Urea is the most abundant of these excretory products, and
it has frequently been assumed that all of the nitrogen excreted in the
urine is thus combined, and allowance is made for the heat of com-
bustion of the amount of urea corresponding to the amount of nitrogen
found in the urine. According to this last supposition, 0.87 calorie
of the energy latent in each gram of digestible protein would be lost
to the body in the urea formed from the nitrogen of the protein." In
a considerable number of actual determinations of the ratio of the
nitrogen to heat of combustion in urine of healthy men made by
Atvater and associates at Middletown, Conn., the average heat of
combustion of the organic matter in the urine corresponding to I gram
of digestible protein amounts to 1.25 calories. In the experiments
here reported the actual heat of combustion was determined in each
instance. The average of these determinations corresponded to 1.20
calories per gram of digestible protein.
The results of the individual tests are given below. Following the
tabular statement of the details of each experiment is a paragraph
showing the nitrogen balance; that is, whether the subject gained or
lost nitrogen during the test. The discussion of the nitrogen balance,
as well as that of sulphur and phosphorus, will be found in another
section of this report (pp. 31-46).
DIGESTION EXPERIMENT NO. 1.
This experiment began with breakfast July 20, 1900, and continued
four days. The weight of the subject (without clothing) at the begin-
fiing was 60.1 kilograms, at the end 60 kilograms.
TABL 3.-Results of digestion experiment No. 1 (serial No. *S4).
Kind of food.
I I I -
I I I-- ------------ --- -- I-
1 : 1 -' 1 _____ ________
During this experiment the subject eliminated 2,550 grams of urine,
containing 57.23 grams of nitrogen. The average balance per day
was therefore: Income in food, 15.82 grams; outgo in urine, 14.31
grams, and in feces, 0.74 gram; implying a gain to the body of 0.77
gram of nitrogen, corresponding to 4.81 grams of protein.
DIGESTION EXPERIMENT NO. 2.
This experiment began with breakfast July 24,1900, and continued
four days. The weight of the subject (without clothing) at the begin-
ning was 60 kilograms, at the end 61 kilograms.
TABLE 4.-Results of digestion experiment No. 2 (serial No. 325).
Kind of food.
Feces (water free)- ---
Per cent digested ..
Nitrogen and heat of
combustion of urine
Energy of food oxi-
dized in the body...
Per cent of energy
. 2,243.4 395 574.2 1,274.2 90.8 13.2
Butter .... ......
Feces (water free) ...
Per cent digested. -
Nitrogen and heat of
combustion of urine
Energy of food oxi-
dized in the body- -
Per cent of energy
I -__ -
I A I
-., ..:!:':c ailii
During this experiment the subject eliminated 3,451 grams of urine,
containing 58.69 grains of nitrogen. This makes the average nitrogen
balance per day as follows: Income in food, 15.82 grams; outgo in
urine, 14.67 grams, and in feces, 0.67 gram; indicating a gain to the
body of 0.48 gram of nitrogen, corresponding to 3 grams of protein.
DIGESTION EXPERIMENT NO. 8.
This experiment began with breakfast July 28, 1900, and
four days. The weight of the subject (without clothing) at
ning was 61 kilograms, at the end 60.9 kilograms.
TABLE 5.-Results of digestion experiment No. 3 (serial No. 326).
Kind of food.
651 Milk__ --------------
MS Feces (water free) ...
Amount digested ....
Per cent digoated -...
Nitrogen and heat of
Energy of food oxi-
dized in the body...
Per cent of energy
x 2 o;
n I S ) ai .3
Grams. Grams. Grams. Grams. Grrams. Calories.
120.7 I 74.5 867.8 25.1 19.32 5,065
272.5 360.6 406.4 61.2 43.66 6,258
1.8 I 139.1 ---....... 4.5 .29 1,282
395 574.2 i 1,274.2 90.8 63.27 12,605
17.4 15.2 34.1 28.3 2.78 519
377.6 559 1,240.1 62.5 60.49 12,086
95.6 97.4 97.3 68.8 95.60 95.9
......- ..... .----- ...-- .-- --.56.65 435
-...... --..- --- --......... ........ ........ 11,651
.....-.............-..----..... .........-------- 92.4
t 1 .4
During this experiment the subject eliminated 4,071 grams of urine,
S containing 56.65 grams of nitrogen. This makes the average nitro-
S gen balance per day as follows: Income of food, 15.82 grams; outgo
I:F in urine, 14.16 grams, and in feces, 0.70 gram, indicating a gain of
S 0.96 gram of nitrogen or 6 grams of protein.
DIGESTION EXPERIMENT NO. 4.
I; This experiment began with breakfast August 11, 1900, and con-
i tinued four days. The weight of the subject (without clothing) at the
beginning was 60.6 kilograms, at the end 62 kilograms.
.. : ii. ..
TABLE 6.-Results of digestion experiment No. 4 (serial No. 327).
Kind of food.
01 Z r B4
Grams. Grams. Grams. Granms. Grams. Gramns.i Grams.
660 Crackers-----.........- 1.20 1,435.1 163.0 100.6 1,171.5 3.9 29.08
652 Milk.....----....--------.... 4,000 500.4 135.6i 170.4 194.4 30 21.8 G
653 Butter -...-----..----- 24 211.4 2.7 208.7 --...... -6.7 .3
.-..--..al.610.2 359.8 1,0j4.4 53 36.14
Total---......----............. 2,146.9 301.3 479.7 1,65.9 70.6 48.19
663 Feces (water free ,.. 70.4 41.2 13.8 11.3 16.1 11.6 2.21
Amount digested ....-........ -1.569 212.2 348.5 1,008.3 41.4 8 38.9
Per cent digested-.... ........ 97.4 98.9 96.9 98.4 78.1 98.9
Nitrogen and heat of '
combustion of urine --..... ----...--- ......- ."... ......... .. .... ----.... 31.28
I Energy of food oxi-
I Per cent of energy .
utilized.................. ......... ............
a Three-fourths of total amount: urine for first day lost.
The urine for the first day of this experiment was lost. During the
remaining three days the subject eliminated 1,990 grams of urine,
containing 31.28 grams of nitrogen. This makes the average nitrogen
balance per day as follows: Income in food, 12.05 grams; outgo in
urine, 10.43 grams, and in feces, 0.74 gram; indicating that the body
gained 0.88 gram of nitrogen, or 5.50 grams of protein per day.
DIGESTION EXPERIMENT NO. 5.
This experiment began with breakfast August 15, 1900, and con-
tinued four days. The weight of the subject (without clothing) at the
beginning was 62 kilograms, at the end 60.8 kilograms.
TABLE 7.-ReRults of digestion experiment No. 5 (serial No. 328).
Kind of food.
652 Milk -..-.............
Grams. Grams. Grams.
480 425.2 48.3
12,240 1,531.2 415
.---..-- 1,956.4 463.3
Feces (water free)..' 123.5 i 81.9 21.8
Amount digested.---. ---....- 1,874.5 441.5
Per cent digested............. 95.8 95.3
Nitrogen and heat of I
combustion of urine:.- ............... .........
Energy of food oxi-
_ died in the body___ ........ .....................
Per cent of energy
utilized ............. .-... -- ......--.. .-........--
Grams. Grams. Grams.
29.8 347.1 10
51.4 594.8 91.8
551.2 941.91 101.8
12.1 48 41.6
539.1 89.9 60.2
97.8 94.9 59.1
74.07 i 11,5
3.48 a .
70.59 10, 14
.. .: f .
.1 0,4 .
. i- -
During this experiment the subject eliminated 7,889 grams of urine,
containing 66.01 grams of nitrogen, making the average nitrogen bal-
ance per day as follows: Income in food, 18.52 grams? outgo in urine,
16.50 grams, and in feces, 0.87 gram; implying a gain of 1.15 grams
of nitrogen or 7.19 grams of protein.
DIGESTION EXPERIMENT NO. 6.
This experiment began with breakfast July 4, 1901, and
four days. The weight of the subject (without clothing) at
ning was 61.45 kilograms, at the end 60.13 kilograms.
TABLE 8.-Results of digestion experiment No. e; (serial No. J3.9).
Kind of food.
Crackers----.. ------. 480
Total--.----_ ---- ------..
Feces (water free) .. i 37.2
Amount digested.... -......
Per cent digested_ I .. _
Nitrogen and heat of I
combustion of urine'. .......
Energy of food oxi-
dized in the body ... -----
Per cent of energy
749.6 | 189.1
1,171.8 1 243.7.
--------- ------------ -
Grams. Grams. Grams. Grams. Calories.
29.7 337.9 8.8 8.74 2,003
260.7 299.8 41 30.29 4.774
290.4 637.7 49.8 39. 03 6.777
4 14. 9 11.7 1.06 205
286.4 622.8 38.1 37.97 6,572
98.6 97.7 76.5 97.3 97
........ ........- ...-.--- ........ 6.228
...... .. -.. 91.8
-I-- ___--- --_I--_
During this experiment the subject eliminated 3,232 grams of urine,
A.: containing 43.77 grams of nitrogen. The average nitrogen balance
per day was therefore: Income in food, 9.76 grams; outgo in urine,
10.94 grams, and in feces, 0.27 gram; indicating a loss of 1.45 grams
i' of nitrogen or 9.06 grams of protein.
DIGESTION EXPERIMENT NO. 7.
This experiment began with breakfast July 14, 1901, and continued
five days. The weight of the subject (without clothing) at the begin-
1^ ning was 60 kilograms, at the end 59.2 kilograms.
ii I,: ..
TA.BE 9.-Results of digestion experiment No.
Kind of food.
Milk ....--....- ..-----
Feces (water free) .--
Per cent digested. -
Nitrogen and heat of
combustion of urine
Energy of food oxi-
dized in the body..
Per cent of energy
7 (serial No. 330).
.. 1,618.2 815.8 391.4 911 72.1 50.55 9-,1
During this experiment the subject eliminated 3,027 grams of uripe,
containing 57.53 grams of nitrogen. This makes the average daily
nitrogen balance as follows: Income in food, 10.11 grams; outgo in
urine, 11.51 grams, and in feces, 0.45 gram; corresponding to a daily
loss of 1.85 grams of nitrogeQ or 11.56 grams of protein.
DIGESTION EXPERIMENT NO. 8.
This experiment began with breakfast July 19, 1901, and continued
five days. The weight of the subject (without clothing) at the begin-
ning was 59.2 kilograms, at the end 60.7 kilograms.
TABLE 10.-Results of digestion experiment No. 8 (serial No. 331).
Kind of food.
656 Crackers-...-....... -
657 Milk .........-----
667 Feces(wate* free) ----
Per cent digested. -
Nitrogen and heat of
combustion of urine
Energy of food oxi-
dized in the body---
Per cent of energy
I i I I i I
, i t,!i
: .:h ......r
.... : ": iii. i
,, ,, ,,
. .... "^ l..
.. : :. .::.
.: mE:. **SS
::it ..:n .
k .. ".E
'i;:.: !:.;xiL ll
- 1 -1-1
:::. ::* :!:
;ii :: ..
d" ::. '
Kind of food.
s5 Crackers- __--------
688 Feces (water free)....
Per cent digested.....
Nitrogen and heat of
combustion of urine
Energy of food oxi-
dized in the body ...
Per cent of energy
During this experiment, which followed No. 8 without intermission
and which was a duplicate of No. 7, the subject eliminated 4,310
grams of urine containing 64.33 grams of nitrogen. The average
daily nitrogen balance was therefore: Income in food, 10.11 grams;
outgo in urine, 12.87 grams, and in feces, 0.43 gram; indicating a loss
of 3.19 grams of nitrogen, or 19.94 grams of protein.
DIGESTION EXPERIMENT NO. 10.
S This experiment began with breakfast July 29, 1901, and continued
three days. The weight of the subject (without clothing) at the begin-
* ning was 59.3 kilograms, at the end 60 kilograms.
During this experiment, which followed No. 7 without intermission,
the subject eliminated 5,223 grams of urine containing 77.62 grams of
nitrogen. This makes the average nitrogen balance per day as fol-
lows: Income in food, 20.22 grams; outgo in urine, 15.52 grams, and
in feces, 1.04 grams; implying a storage in the body of 3.66 grams of
nitrogen, corresponding to 22.87 grams of protein.
DIGESTION EXPERIMENT NO. 9.
This experiment began with breakfast July 24, 1901, and continued
five days. The weight of the subject (without clothing) at the begin-
ning was 60.7 kilograms, at the end 59.3 kilograms.
TABLE 11.-Results of digestion experiment No. 9 (serial No. 332).
28 .. ..
TABLE 12.-Results of digestion experiment No. 10 (serial No. 888).
Kind of food. o o d .
Crackers............--- 00 I 813.3
Milk ..................I-------------- 9,000! 1,152.0
Total ............. ---- 1,965.3
Feces (water free) ..' 100.3 68.1
Amount digested--.--..--...- 1,897.2
Per cent digested--...--'....... 96.5
Nitrogen and heat of
combustion of urine ................
Energy of food oxi-
dized in the body.. ........ .........
Per cent of energy I
utilized ... .... -.
Grams. i calories.
This experiment followed No. 9 without intermission. The diet
was nearly the same as in No. 8. During the three days of this experi-
ment the subject eliminated 4,290 grams of urine containing 49.74
grams of nitrogen. The average nitrogen balance per day was there-
fore: Income in food, 20.70 grams; outgo in urine, 16.58 grams, and
in feces, 1.05 grams; indicating a gain of 3.07 grams of nitrogen,
corresponding to 19.19 grams of protein.
RESULTS OF DIGESTION EXPERIMENTS.
In Table 13 are summarized the results obtained in the various
experiments on the digestibility of the total food eaten. Although the
diet was composed in each case of bread (in the form of soda crack-
ers) and milk, with butter in some cases, the relative proportions of
these two food materials, as well as the quantities taken, varied in
the different experiments, as will be seen from the details of the
experiments given above.
TABLE 13.-Coefficients of digestibility of nutrients and availability of energy.
Kind of food.
Bread, butter, and milk --------.
Bread and milk .......--......-.........
.....do.--. --.....--- ... ....-...-- -------..
d o ----. .------------ ----------- -- ---
-.----do ---- -- -- ---- ---------------- -----
Per cent. Per
Per cent. p i
92.4 .. :
:.... 3'i .
.. m. .. .. ....
::.: .:" ii...::
Grams. Grams. Grams.
58.4 660.4I 20.9
407.7 450.9 63.0
466.1 1,111.8 83.9
10.5 37.9 32.2
455.6 1,073.4 51.7
97.1 96.6 61.6
As explained above, the experiments were varied in order to study
the digestibility under different circumstances, so that an average of
the results obtained would have little value except as these variations
are taken into consideration. It will be noted that the results of
experiment No. 6 differ markedly from all the others in the larger per-
centage of the protein digested, the digestibility of the fat being also
increased but not to such a marked degree. This result is not due to
the relative proportions of bread and milk in the diet, since in this
respect the experiment is intermediate between experiments Nos. 5
and 7. The amount of protein taken in the food was somewhat less
than in experiment No. 7, and very much less than in experiment No.
5. This fact would of course be favorable to the more complete absorp-
: tion of the protein, as would also the circumstance that during the
week previous to the test the subject had eaten less food than usual.
These circumstances may account for the rather unusual figures
obtained in this period, and as the feces were collected, dried, and
weighed by the subject himself it would seem improbable that any
serious loss could have occurred without being detected. Neverthe-
less, the amounts of total dry matter, nitrogen, and phosphorus found
in the feces for this period are so small that the results are given with
some hesitation, and in comparing the determined and calculated fig-
ures for digestibility we have averaged the experiments both with and
S without No. 6.
STable 14 shows for each experiment and for the average of all the
experiments: (1) The percentage of protein actually digested, as deter-
mined; (2) the digestibility as calculated, assuming that 85 per cent of
the protein from cereals and 97 per cent of the protein from milk were
S digested, and (3) the figures calculated on the assumption that 90 per
cent of the protein of the bread and 97 per cent of the protein of the
milk were digested.
TABLE 14.--Coeficients of digestibility of protein, calculated and determined.
Results cal- Results cal-
culated, as- culated, as-
sumingthat suming that
Results 85 per cent 90 per cent
actually of bread pro- of bread pro-
a u dy tein and 9 tein and97
on percent per cent
of milk pro- of milk pro-
tein were tein were
E: Percent. Percent. Percent.
i Experiment No. 1 -........ ............. ........... ......... 95.3 93.3 94.9
Experiment No. 2 .............. ........... .... ................... 95.8 93.3 94.9
Experiment No.2 ------------------------------------------9R5. 8 93.3 94.9
S Experiment No. 3 ----...............--.--------- .. .....- -....... 95.6 93.3 94.9
Experiment No. 4--..........- ..--............................. 93.9 90.5 93.2
S Experiment No. 5..----..--..--.. ...---...---..--.....--....... 95.3 95.8 96.3
Experiment No. i ---------------------------------------9".3 93.9 95.3
Ii zperiment No. ............................................... 97.3 93.9 953
S Experiment No. 7 -....---......------............-............. 95.5 94.0 95.3
Experiment No. 8 ... ------.--------------------.....--------. 94.9 94.0 95.3
Experiment No. 9 .-- ----...-.....--- ...---................... 95.7 94.0 95.3
Experiment No. 10-------.. --.. --... -----... ---.........--...... 94.9 94.0 95.3
S Average of all............................................ 95.4 93.6 95.1
Average, omitting experiment No. 6 .---..--------------95.2 93.6 95.0
It will be seen that the digestibility of the protein of the diet, as cal-
culated on the assumption that 85 per cent represents the digestibility !
of bread protein and 97 per cent that of milk protein are in 9 out of the "ii"
10 cases noticeably lower than the results actually obtained, the aver
age being 1.8 or 1.6 per cent lower than the average actual value,
according as we do or do not include experiment No. 6.
If, however, we assume that 90 per cent of the bread protein was
digestible, and use the same factor as before (97 per cent) for the milk, .
we find that (with the exception of experiment No. 6) the calculated
and determined values agree in every instance within 1 per cent,
while the averages agree within one-quarter of 1 per cent, a varia-
tion which may well be considered as negligible.
The factor 90 per cent for the digestibility of the bread protein was
suggested by the fact that this is about the value found for white
bread by Woods and Merrill a in an extended series of experiments
with a number of different subjects, and also in tests with one of the
four subjects employed by Snyder.6
As might be expected from the fact that fat is supplied in an emulsi-
fled and readily available form in milk, its digestibility in these
experiments was rather higher than is usually found. A detailed
comparison, such as that given for the protein, is, however, impracti-
cable, (1) because of the impossibility of distinguishing between ani-
mal and vegetable fats in the crackers used, and (2) because those
portions of the feces designated "fats" and "carbohydrates" really
consist largely of other substances.
During experiment No. 2, in which the diet was the same as in
experiments Nos. 1 and 3, there was (as will be more fully described
beyond, p. 35) a very considerable loss of sleep. This, however, does !
not seem to have had any appreciable effect upon the proportion of
either of the nutrients digested.
Experiments Nos. 7, 8, 9, and 10 throw some light upon the digesti- l
ability of liberal and restricted diets. These were carried out in series,
and the relative proportions of milk and bread were uniform through-
out. The amount eaten per day was, however, twice as great in
experiments Nos. 8 and 10 as in experiments Nos. 7 and 9. On the
smaller diet the percentage digested was slightly higher. The differ-
ence is quite small, less than 1 per cent, but as all other experimental
conditions were carefully maintained uniform, and as the agreement.
between the similar experiments is almost complete, it would seem
that the better digestibility shown by experiments Nos. 7 and 9 over
experiments Nos. 8 and 10 must be attributed to the fact that less
food was taken. Larger but more variable differences have already 7i
been observed by Snyder (loc. cit.) in similar experiments.
Experiments Nos. 7 to 10 were carried out without intermission, and
a U. S. Dept. Agr., Office of Experiment Stations Bul. 85, p. 32.
b U. S. Dept. Agr., Office of Experiment Stations Bul. 101, p. 83.
covered a period of eighteen days. Experiments Nos. 1 to 3 covered
similarly a period of twelve days. The results obtained from these
experiments make it evident that an extremely simple diet may be
continued for a very considerable number of days without necessarily
diminishing its digestibility.
COMPARISON OF THE METABOLISM OF NITROGEN, SULPHUR, AND
S.:As has been explained, the experiments above discussed as diges-
tion tests were also designed to include a study of the comparative
metabolism of nitrogen, sulphur, and phosphorus. In each experi-
ment the diet was uniform and the urine for each twenty-four hours
was collected and examined. Aliquot portions of each day's urine
were mixed to give a composite sample representing the entire period.
Nitrogen was determined in the urine of each day, and the results
were verified by the analysis of the composite sample.
Phosphates in the daily urines were determined volumetrically by
titration with standardized uranium acetate solution in the usual
S manner. The total phosphorus of the urine for the whole period was
determined as described in the section on analytical methods, above.
It will be seen from the results as tabulated below that the sum of the
figures obtained by titration of the daily urines ranges in the different
S experiments from 95.5 to 98 per cent of the total by the gravimetric
method in the composite for the period. These variations are very
S likely due as much to errors in the volumetric determinations as to
differences in the amount of "organic" phosphates present. If the
methods and manipulation were free from error the results would
indicate from 0.02 to 0.05 gram of phosphorus (or 0.04 to 0.12 gram
PO,2) per day eliminated in forms not precipitated by uranium. This
amount is so small that it appears quite sufficient to use the volumet-
rie method when one desires merely to follow the general course of
the phosphorus excretion, determining the total phosphorus by the
standard gravimetric method in cases where an accurate balance of
income and outgo is to be determined. In this connection it may be
noted that recent investigations by Ceconi and others a of the so-called
organic phosphates of the urine have given quite variable results
and have not tended to emphasize the importance of the small amount
of phosphorus thus combined.
SOn account of unavoidable interruptions it was impossible in the
experiments carried out in 1900 to determine sulphur in the urine of
each day. The amount of total sulphur and of sulphate sulphur was,
however, determined for each period. The same determinations were
i 7 Verhandl. Cong. Innere Med. Rome, 1896; abs. in Jahrb. Thier.-Chem., 27
S(1897), p. 362. Jolly, Compt. Rend. Acad. Sci. Paris, 127 (1898), p. 118. Oertel,
Ztschr. Physiol. Chem., 26 (1898), p. 123. Keller, Ibid., 29 (1900), p. 146.
included in experiment No. 6. In experiments Nos. 7 to 10 the sul-
phate sulphur was determined for each day and the total sulphur for
each period. Comparing the sulphate" and "total" sulphur in the
different experiments, it would appear that from 83.1 to 89.6 per cent.
of the sulphur in the urine was in the form of sulphates. The sulphur
in forms other than sulphates-so-called "neutral" sulphur-has
recently been studied by Reale and Velardi,a Harnack and Kleine,b
Freund,c Petry,d and doubtless others, and will probably repay fur-
ther investigation. In the present experiments, however, time did
not permit of any study of this question. Neither did the analyses
include the separate determination of the ethereal sulphates which,
as the protein consumed came principally from milk, were probably
present in less than the usual proportions.e
The final results of the examinations of the urine are brought
together in Table 15, which shows the data for each experimental
day, as well as the total for each of the ten periods. Partial analyses
of the urine for the four days immediately following experiment No.
5 are also given.
TABLE 15.-Data of examination of urine in experiments Nos. 1-10.
imentDate amount Specific
iment Date. amount gravity.
num- voided. gray.
1-...- July 20-21-- 817 1.0280
I TJ.I 01 91- ;1 1 02r0n
Ju lyJ z1-=k --- --.----
July 23-24 ---..----
July 24-25 ---------
July 30-31--. ..-
July 31-August 1 ..
3,550 ......- ....
782 i 1.0300
S 670 1.0305
gen. Assul- Total Byti- Total.
Grams. Grams. Grams. Grams. Grams.
15.38 ...--.-- ........ 1.30 /.......
13.89 ------- 1.34 .......
14.28 .......-- ....----- 1.40 ..--
13.68 --------1---- 1.41
13.68 ........ ........ 1.41 .-.-- -
57.23 3.37 3.801 5.45 .5.63
13.96 1.-------28 --------
14.04 .-------------- 1.34 --..----
15.63 _-_----_- ------- 1.43 ..---...
15.06 -.......- ..... 1.66 ......
58.69 3.46 3.86 5.71
15.65 ------.--.-----. 1.51
,13.67 !.--.---- --..---- 1.34
13.51 ------. ..------ 1.26
13.82 .--...--..-....--- 1.40
56.65 3.24 3.74 ( 5.51
10.19 .......-- -----.94
10.92 .... ... .. 1.06
10.17 ........ .. 1.02
Total-..----- 1,990 ..-- 31.28 1.85 2.16 3.02 3.10 257.7
5....... August 15-16 ..... 2,180 1.0130 15.12 1.48 --------110.6
August 16-17....... 2,130 1.0120 16.07 -1.72 -------117.4
August 17-18---..-- 1,859 1.0145 16.98 ........ 1.79 ------... 127.3
August 18-19...... 1,720 1.0150 17.84 ..--.-- ..---- 1.78------ 131.8
Total--....-- 7,889 --.....--. 66.01 i 3.94 4.48 6.77 6.96 487.1
a Studii di clinic medical, Napoli, 1895; abs. in Arch. Verdauungskrankh., S
(1896-97), p. 141.
b Ztschr. Biol., 37 (1899), p. 417.
e Ztschr. Physiol. Chem., 29 (1900), p. 24.
d Ibid., 29 (1900), p. 45.
e See results by Laquer, Verhandl. Cong. Innere Med., 16 (1898), p. 546; abs. in
Jahrb. Thcir.-Chem., 28 (1898), p. 336.
; "... :::::ii;;;ii:...l
.. ...:...... ....
.... ... ..
* *: .,...... i::".:.., ,
::E ":. !
S :ii 2 "
1|i,, TABLE 15..-Data of examination of urine in experiments Nos. 1-10-Continued.
August 21-22 ......
6------....... July 4-5............
July 5-6 -........
....... July 14-15.........
---.... July 19-20.....----
July 21-22------- .
July 22-23 ..........
.--...... July 24--25..........
July 31-August 1 ..
11.45 ... .....
790 1.0280 12.64 .77
783 1.0290 12.57 .75
936 1.0270 13.01 .79
902 1.0240 12.73 .72
899 1.0260 12.88 .78
By ti- Total. bus-
tration. Total t ion.
Grams. Grams.: Cals.
1.70 ........ ........---
1.71 .. ....
1.71 ........ .-------.......
6.86 ........ ........
1.01 1... .-.1.-.- ...
1.21 ...-..... ...--------
4.28 4.46 | 35J.3
.84 I .. .-
.88i -. ..... ...
.99 ........ ........
4.75 i 4.98 1 439.8
..-.- .. 1.43 ......- ..........
........ 1.42 ..--...... '--------........
....... 1.57 !.......
5.28 7.21, 7.44 605.9
------...... 1.25 .- -. .-...-----
-. -1.21 ........ ........
4.33 6.29 6.59 478.8
........ 1.33 ........ I ......
.. .lm. 1.44 '
.... .. 1.51 ......-.. .
3.64 4.28 4..46 374.1
With the exception of experiment No. 6, the experiments fall into
three series, as will be seen from the dates given in the table. The gen-
eral occupation and habits of the subject were similar in all, except
as modified for the experiment in which the effect of loss of sleep was
studied, and have already been described. The first series included
three four-day experiments (Nos. 1, 2, and 3) carried out in the later
part of July, 1900. The bread and milk diet was taken for a day and
a half before the beginning of the first experiment. The diet was
entirely uniform throughout, except that on the first day 60 grams
Sand on the second day 20 grams of butter were taken, after which 40
Grams per day were taken throughout. The fuel value of the diet was
Sthus a little above the average on the first and a little below the aver-
age on the second day, but was the same for each of the three periods,
r 9861-No. 121-02- 3
-- ----- ~"'
and except for this slight variation in the amount of fat taken on the
first two days the daily diet was uniform throughout the twelve days
covered by the series.
The second series, including experiments Nos. 4 and 5, was begun ten
days after the conclusion of the first series. During most of the inter-
vening time the subject had followed the usual routine and lived on a
rather simple mixed diet consisting largely of bread, milk, and fruit.
Three days shortly before the beginning of experiment No. 4 (August 7
to 9 inclusive) were, however, spent in another place and under some-
what different conditions, the work being more active and the diet
more abundant and varied, and consisting more largely of meat.
Experiment No. 4 was really begun on the morning of August 11, and
the feces collected correspond to a period of four days. Unfortu-
nately the urine of the first day was lost, so that as a metabolism
experiment it covers only three days preceded by a day in which
exactly the same diet was taken. In calculating the balance of income
and outgo for the three days it is assumed that the elimination of feces
was practically uniform. As compared with the preceding experi-
ments the diet in experiment No. 4 was about normal as regards fuel
value but low in protein. While this diet was evidently sufficient for
the needs of the body, the large amount of bread and butter was not
appetizing to the subject, who during this experiment felt a little less
vigorous than usual, though perfectly well. After four days on this
diet experiment No. 5 was begun, the diet being changed by omitting
the butter, reducing the bread to less than one-third and greatly
increasing the amount of milk, so that the diet had nearly the same
fuel value as in experiment No. 4, but furnished over 50 per cent '
In the third series (experiments Nos. 7 to 10) carried out in July,
1901, the diet was qualitatively uniform throughout the eighteen days
coveredrthat is, the diet, consisted of bread and milk in the same 4
relative proportions. The amounts taken daily were, however, twice
as great in experiments Nos. 8 and 10 as in experiments Nos. 7 and
9. The daily routine was similar to that followed in the preceding
experiments, except that the experimental day was begun at 7.30
a. m., instead of 6.30 a. m. -
The results obtained can be best discussed by considering sepa-
rately the different points on which the experiments were designed to
throw some light.
INFLUENCE OF LOSS OF SLEEP.
Roeskea as the result of an extended study of the course of the
phosphorus excretion during the day concluded that the degree of
a Ueber den Verlauf der Phosphorsaure-Ausscheidung beim Menschen. Inaug.
Diss., Greifswald, 1897.
mental and vital activity, and especially the alternation of sleeping
and waking periods, had a greater influence upon the excretion of
phosphorus than did the food ingested. Thus, when the urine was
Collected and the phosphorus determined for each two-hour period
from the time of rising-0 a. mn.-till that of retiring-11 p. im.-the
H curve representing the excretion was quite similar from day to day.
SThis normal course of the excretion was not greatly altered by chang-
ing the diet or even by omitting a meal entirely, but was strikingly
. changed when the subject, rose two hours before the usual time in the
Morning. The food and feces were not analyzed and apparently the
diet was not the same on the different "normal" days, so that the
Conclusions were necessarily based more largely upon alterations in
the form of the curve representing the excretion than upon the total
amount excreted during the day, and as neither nitrogen nor sulphur
was determined there is nothing to indicate whether or not the
changes in phosphorus metabolism accompanied similar changes in
the metabolism of proteid material. In view of these questions it
seemed desirable in beginning the present investigation to give some
attention to this matter, in order to ascertain whether unusual pre-
cautions as to regularity of hours would be necessary in experiments
in which the metabolism of phosphorus was to be studied in com-
parison with that of nitrogen. This point was studied by greatly
reducing the time spent in sleep in experiment No. 2, all of the other
conditions (which have already been described) being the same as in
experiments Nos. 1 and 3. Experiment No. 1 ended and experiment
; No. 2 began with breakfast of July 24, 1900. That night, the subject
slept but two and one-half hours, the following night four hours, and
the third night no sleep was taken. The subject then returned to
his usual routine, sleeping about seven hours each day. The waking
Hours of the first night were spent upon mental work of the kiid to
which the subject was accustomed. On the second and third nights,
after the usual hour of retiring, the time was passed in reading light
: literature. Only on the second night was there difficulty in remain-
ing awake. Throughout each day and until 10 or 11 o'clock in the
evening the subject was engaged upon his usual duties and did not
Feel any distinct effect of the loss of sleep, except a slight nervousness
on the day following the third night-that on which no sleep was
The loss of sleep resulted in an increased elimination of each of the
three elements studied, but as the sulphur was determined simply by
periods, only the nitrogen and phosphorus can be compared in detail.
It will be seen from Table 15 that the increased elimination does not
appear until after the second night and then continues for two days
after-the return to the usual routine, thus running over into the follow-
ling period (experiment No. 3). The results are best shown, therefore,
not by a comparison of the totals for the three periods, but by aver-
aging the days in which the increase is found actually to have occurred
and comparing with the preceding and following days. Thus we find
for five "normal" days, beginning July 21, an average of 13.97 grams
nitrogen and 1.355 grams of phosphorus, with the following ratio:
N : P :: 100 : 9.66. The following three days, which show the effect
of the loss of sleep, average 15.45 grams nitrogen and 1.538 grams
phosphorus, with a ratio of 100 : 9.96; while the three days next fol-
lowing, when the elimination is again normal, average 13.67 grams
nitrogen and 1.328 grams phosphorus, the ratio being 100 : 9.65.
In view of the amount of sleep lost the total increased elimination
seems quite small both in the case of nitrogen and that of phosphorus,
and it is evident that the latter was only slightly more affected than
the former, since the change in the ratio is no larger than would often.
be found on comparing successive "normal" days when all the condi-
tions appear to be uniform.
The relative fluctuations in the amounts of nitrogen and phosphorus
eliminated daily during this series .is shown graphically in fig. 1, in
which the solid line represents the excretion of nitrogen and the dot-
ted line that of phosphorus.
The elimination of sulphur as measured by the four-day periods ran
very closely parallel with that of nitrogen throughout this series, the
ratio N : S being in the first period as 100 : 6.64, in the second as
100 : 6.58, and in the third as 100 : 6.60.
LAG OF ELIMINATION AFTER CHANGE OF DIET.
A considerable number of experiments upon the time relations of
the elimination of nitrogen, sulphur, and phosphorus after the inges-
tion of proteid food have recently been made in the laboratories of
Wesleyan Universitya and in the papers recording the results, the
earlier experiments upon this question are also discussed. The gen-
eral plan followed in these studies is to place the subject upon a
diet and routine similar to that followed in the first series of experi-
ments here recorded, and then to collect and analyze the urine for
every three hours, or in some cases every hour and a half, during the
day, the night urine being collected in a single nine-hour period.
The diet, and routine are strictly maintained until the urinary excre-
tion has been found to be practically uniform for two or three days.
The subject then takes with breakfast either in addition to the regu-
lar food or in place of an isodynamic amount of butter or other food,
enough lean beef to furnish the desired amount of extra protein. All
a Sherman and Hawk, Amer. Jour. Physiol., 4 (1900), p. 25; Atwater and Hawk,
unpublished material: Hawk and Chamberlain. unpublished material.
other conditions remain unchanged and the urine is collected and
analyzed by short periods as before, this being kept up until all
changes in the urine resulting from the ingestion of the extra foad
have disappeared. The tests made with d ilferent subjects and in dif-
ferent years show slight variations in some details, but the general
results agree. Very soon after the ingestion of the extra food there
is a rise in the rate of excretion of nitrogen as compared with that
S found in the corresponding periods of other days. This rise is rapid
and the time required to reach a maximum depends upon the amount
. .... -- .- -- -- ---..,..i,...--- -
EXPERIMENT NOI EXPERIMENT N2 EXPERIMENT N-3
DAYS 1-4. DAYS 5-8. DAYS 9-12.
FIG. 1.-Diagram showing fluctuations in the daily excretion of nitrogen and phosphorus during
the first series of experiments (Nos. 1-3). In platting these curves the periods of time are rep-
resented by the abscisste, while the ordinates represent the excretions expressed in percent-
ages of the average rate found on the normal days. The short horizontal lines below the
curves show the nights in which the losses of sleep occurred.
of extra protein ingested. With 5 grams of extra nitrogen the maxi-
mum was reached in from three to four and one-half hours; with 10
grams, generally in from six to nine hours. The fall in the rate of
excretion -was much less rapid than the rise, but usually the normal
Rate was regained before the end of the second day. The general
features of the curve representing the elimination of the extra nitro-
gen were the same when the subject was gaining as when he was los-
ing nitrogen and were the same when the beef was simply added to
the regular diet as when it was substituted for an isodynamic amount
of butter. In general the sulphates and phosphates eliminated were
increased simultaneously with the nitrogen. All of these experiments
had to do with the increased elimination brought about by the inges-
tion of extra protein with a single meal. Some of the present experi-
ments were arranged with a view to studying the "lag" in the elim-
ination when the diet was suddenly changed and the new diet
maintained for several days.
On passing from the diet of experiment No. 4 to that of experiment
No. 5, there was little change in fuel value, but the amountsof nitro-
gen and phosphorus ingested were largely increased. Under these
conditions there was a "lag" of some days, i. e., some days were
required before the rate of elimination become approximately uniform.
Experiment No. 4 lasted three days and although experiment No. 5
properly continued but four days, the diet was maintained and the
elimination of nitrogen and phosphates determined for an additional
fpur days. The course of the excretion of nitrogen and phosphorus,
for the eleven days is shown in fig. 2, in which the curves are platted
in the same manner as in fig. 1 above.
It will be seen that while the phosphorus elimination reaches a
maximum on the third day, the maximum elimination of nitrogen is
reached only on the sixth day. It must be noted, however, that the
increase of phosphorus in the diet was considerably greater in pro-
portion than the increase of nitrogen, so that although the curves
meet on the fifth day it does not follow that equilibrium was then
restored. When the elimination of phosphates was at the maximum
there was a storage of phosphorus in the body, whereas during the
maximum elimination of nitrogen the body was losing that element,
The body was in fact nearly in nitrogen equilibrium when the maxi-
mum elimination of phosphorus was reached.
In experiments Nos. 7 to 10 the lag was studied under different cir-
cumstances from those just described. Instead of attempting to keep
the fuel value approximately uniform while changing the amounts of
certain constituents, the diet was here kept qualitatively the same, so
that every change affected each of the constituents to the same extent.
The general outline was as follows: For five days the subject took a
restricted diet, which it was thought would be just about sufficient to
enable him to do his usual work without becoming uncomfortably
hungry. As a matter of fact there was practically no sensation of
hunger, but the subject lost during the five days somewhat over 9
grams of nitrogen and about 2 pounds in weight. During a second
period of five days twice the original diet was taken. Then the sub-
ject returned to the original diet for another period of five days, the
object here being to study the lag after a decrease as well as after an
increase in the diet. At the end of the third period the diet was again
doubled, and the double diet was this time maintained for three days.
The results for the eighteen days covered by this series of experiments
... ...... .. ....,.. ... .. ..
.i; ;... .
:. .:,.::-:: -.. ii
?* ":: ...E.. :dEI
: *:. : iEE *:
* ,," iMivl~
Eq:ii; i i
are shown in fig. 3, in which the curves are platted in the same manner
as in figs. 1 and 2. In this case the1 sulp)hatt( sulphur wIas also deter-
mined, and is represented in the figure ty a broken line, nitrogen and
phosphorus being represented respectively by solid and dotted lines.
The rises and falls in the curves in this figure on passing from one
experimental period to another are not large as compared with the
PmG. 2.-Diagram showing fluctuations in the daily excretion of nitrogen and phosphorus during
the second series of experiments (Nos. 4 and 5 The curves are platted in the same manner
S as those in fig. 1.
Change in the diet. Thus the diet in experiment No. 8 was twice as
: great as in experiment No. 7, but the greatest daily elimination was
only about one-half larger for nitrogen and sulphur and two-thirds
larger for phosphorus. This is mainly because, as would be expected,
! there was a loss of body material on the small diet and a gain on the
Large diets. The daily gains and losses are shown in Table 16, the
': complete balance for each experiment being tabulated beyond.
15 0 -........ 7
10 0 2*
E XPERIlMEN T N97 E XPERIlMEN T N2 8 E XPERIlMENT N2 9 X T N21
DAYS 1 -6,. DAYS 6 10. D AYS I I- I, AS5S-I
FI. B.-Di" grm showing fluctuations in the daily ex eretion of nitrogen, sulph ur, and phosphortmu during the third series of experimms(o.710.Tecre
are plattd aIn atba, smae manner as those 1 ina 1 1 1 and. S. Tike rate o f elimination of nitrogen Is repre sented by7 the solid, that of theiuhrbteboknad
As has already been stated, the total sulphur and total phosphorus
eliminated by the kidneys during each period were determined by
analysis of a composite sample of urine. The sulphate sulphur and
the phosphorus precipitable by uranium acetate were determined
both in the composite sample and in the urine of each day. From
Sthe data thus found it is easy to estimate the total sulphur or total
phosphorus for the urine of each daly if we assume that the ratio of
, "unoxidized" to total material is constant during tlhe experimental
period. While slight errors might result from this assumption, they
woulu uo mar too smau to arIecutL ble present ulisussi ui. i jne ama ounts
thus estimated are therefore used in the following table:
TABLE 16.-Daily gains and losses of nitrogen, sulphur, and phosphorus in experi-
ments Nos. 7-lu.
.. Nitrogen. I Sulphur. Phosphorus.
ont Date. Gain(+)! Gain (+) Gain (+)
bimi .In urine, or In urine. or In urine. or
IE 'loss (-). loss (-).| loss (-).
Grams. Grams. Grams. Gram. i Grams. Gram.
-i-;-? ::.. ... July 14-15 ...................... 11.65 -1.99 0. 82 -0.16 1 0.88 +0. 10
July 15-16...----------------- 11.12 -1.46 .81 .15 .92 + .0i
-July 16-17----------------.. 11.35 -1.69 .87 .21 1.05 .06
July 17-18.. ----------------- 11.66 -2 .82 .16 1.09 .11
July 18-19------------9--.--- 11.75 -2.09 .83 .17 1.05 .07
..... July 19-20 ..------------.... 14.83 +4.'5 1.04 + .27 1.23 + .51
July 20-21-----------.................-- 15.81 +3.37 1.00 + .31 1.48 + .2
I July 21-22.................... 15.19 +3.99 1.00 + .31 1.47 + .27
:: July 22-23--..---.-------...--... 14.91 +4.27 1.08 + .23 1.65 + .09
July 23-24..---......------..--- 16.88 +2.30 1.16 + .15 1.62 +. 12
,' ...... July 24-25 --...-...--...----.. 12.64 -2.96 .89 .23 1.31 .23
SJuly 25-26-...--.......--------- 12.57 -2.89 86 .20 1.2i .19
F July 2-27---..........---------.........-- 13.01 -3.33 .91 -.25 143 35
July 27-28-..-...... --- ... 12. 73 -3.05 .83 .17 1.31 23
July 28-29----. .------------- 12.88 -3.20 .90 .24 1.27 .19
S10.-- July 29-30----------------- 16.23 +3.56 1.19 + .07 1.39 + .50
i July 30-31 .------------------ 16.71 +2.94 1.23 + .03 1.50 + .39
: July 31-Aug. 1------------- -- 16. bO +2.85 1.22 + .04 1.57 + .32
It will be seen from this table that the gains and losses were con-
Ssi'derable, and that equilibrium was not reached in any experiment,
i even after the continuance of a uniform diet for five days. In view
of the large amounts of material gained and lost there is danger that
any inferences in regard to lag which could be drawn from these
results might be subject to unknown errors arising from the breaking
downn of body material on ihe one hand or the transformation of food
protein into body protein on the other. It will be shown, however,
Sthat, except in cases where the balance was evidently affected by the
!'aUg, the proportion of sulphur to nitrogen was nearly the same in the
aJterial stored or lost as in the food material actually absorbed.
iWith phosphorus the variations are larger, but a similar relation
pears to exist. Hence the question of lag is quite as important
ihee asin the cases where it has been more especially studied, but
fre it represents not merely the time required for the metabolism of
Ingested materials, but to some extent also the time necessary
te body to adapt itself to the increased or decreased diet. On
passing from the insufficient diet of experiment No. 7 to the abundant
diet of experiment No. 8 the nitrogen elimination rises on the first
day and then remains nearly stationary for three days, during which
a large amount (of nitrogen is stored, as though the body during these
days was replacing the protein previously lost. Then on the fifth day
the elimination again arises, though not far enough to establish nitrog-
enous equilibrium. The elimination of sulphur rises somewhat more
sharply on the first, day than that of nitrogen, then continues about
uniform for two more days, and begins to rise again on the fourth day,
continuing to rise on the fifth and reaching a relative rate somewhat
higher than that of the nitrogen. The sulphur curve is therefore
similar to the nitrogen curve, but the changes are somewhat more
marked, and in one case appear to begin earlier. The phosphorus
rises sharply during the first and second days and again on the fourth
day. What has been suggested with reference to the nitrogen and
sulphur appears to be true to a lesser extent of the phosphorus. The
increased diet immediately increases the excretion, the increase in
this case continuing two days, then for a short period-in this case
one day-the elimination is nearly constant, while a considerable pro-
portion is stored in the body, after which the rate of elimination again
rises. While the phosphorus does not reach equilibrium as regards
income and outgo, it more nearly approaches this condition than
either the nitrogen or the sulphur.
When the diet was reduced to one-half, the rate of elimination of
each of the three elements studied fell sharply on the first day and
showed little if any fall thereafter. Thus, in each case the elimination
lagged less in falling than in rising. This is the more striking, in view
of the fact that the elimination of both nitrogen and sulphur was
rising at the time the change in diet was made.
In the final period, when the double diet was again resumed, the
changes in rate of elimination were similar to those found in the first
instance, except that the rise shown by the sulphur was somewhat
more pronounced. Pressure of other work prevented the continuance
of this experiment after the third day.
A somewhat marked but temporary increase in the phosphorus
elimination will be noticed on the third day of experiment No. 9, and an
examination of the curves shows that simultaneously there occurred
a smaller but distinct increase of sulphur, and an increase of nitrogen
which relatively is much smaller still and would scarcely have been
noticed had only the nitrogen metabolism been studied. Although
careful note had been taken of anything which seemed likely to affect.
metabolism, it is difficult to assign a reason for this increase. During
the early parts of the two preceding nights there had been slight rest-
lessness, which was attributed to the warm weather, but previous
experiments had indicated that simple loss of sleep, even when very
marked, had no great influence upon tlhe metabolism of this subject
S* ..... ****;f..
.. .. ".:: .
.. .. .. : .."
:i.E :i '.:...
and increased the relative amount of phosphorus little, if any, more
S than that of nitrogen. Such instances as this would seem to lend some
support to the view, apparently quite goe erally held, that thel nervous
condition of the subject has a greater influence upon the metabolism
Sof phosphorus than upon that of nitrogen. A factor which is perhaps
liable to be overlooked in such cases is the influence of the degree of
alkalinity of the blood upon the elimination of phosphates through
COMPARISON OF BALANCE OF INCOME AND OUTGO.
l It is now generally recognized that the daily balance of income and
outgo of nitrogen in the human organism may be influenced by a
Variety of factors, some of which can not be controlled or even satis-
Sfactorily defined. The same is doubtless true of sulphur and probably
.* td a greater extent of phosphorus. In general, it is believed that in -
-H: the present experiments the metabolism was comparatively free from
the influence of such obscure factors, but ii interpreting the figures
Obtained for the balance we must take into account (1) actual errors
in the determination of income and outgo, and (2) the elimination on a
give day of material whose katabolisn is to be attributed to the diet
or other conditions of some preceding day or days-in other words,
the "lag" in the elimination. Errors in determination of income and
outgo fall into two groups-analytical errors, and losses of material.
The analytical work was carefully performed by the methods already
described. In several cases the constituent sought was present in
very small amount, which must have increased the relative errors,
and it may be stated that in the opinion of the writer the determina-
tions of sulphur were less satisfactory than those of nitrogen and of
phosphorus. As regards the loss of material, it is believed that no
appreciable mechanical loss of either food or excretory products could
have occurred in any of the experiments, but there may have been
larger losses through the perspiration. As the experiments were all
made in summer and only one-third to one-half of the ingested
water appeared in the urine, considerable quantities of water must
have passed through the skin, and more or less loss of the elements
studied doubtless occurred in this way. The elimination of nitrogen
through the skin has been briefly discussed in a previous bulletin,a
where it is shown that different estimates of the amount which may be
Stthus lost per day vary from 0.2 gram to 1.36 grams. Very little data
seems to be available from which to form an idea of the amounts of
sulphur and phosphorus which may have been lost through the skin.
Favreb found in the perspiration only traces of phosphates, but
reported one-fourth as much of alkaline sulphates as of urea, corre-
GU. S. Dept. Agr., Office of Experiment Stations Bul. 98, p. 51.
SCompt. Rend. Acad. Sci. Paris, 35 (1852), p. 721; Schaffer's Text-book of
,hysiology, Vol. I, 1898, p. 671.
spending to an elimination by the skin of about 1 part by weight of
sulphur to 8 parts of nitrogen.
Little can be said regarding the amounts of nitrogen and sulphur 4
given off as volatile compounds by the intestine or lost in drying their
feces in the air at 1000 C. It is known that some nitrogen is thus lost
from the feces, probably mainly as ammonia. Loss of ammonia may
be avoided by adding acid before drying, but this would result in a- :
loss of sulphur present as sulphids. Hydrogen sulphid is stated to
be a normal constituent of the intestinal gases, but the amount. of
sulphur lost from the body must have been very small in these experi-
ments. It follows from what has been said that, aside from any errors
of manipulation or analysis, the figures given for nitrogen and sulphur
in urine and feces do not quite represent the total outgo from the
body. The average daily balance, as actually determined for each
experiment, is given in Table 17.
TABLE 17.-Balance of income and outgo of nitrogen, sulphur, and phosphorus-
average per day.
Nitrogen. Sulphur. Phosphorus.
Experi- value of ."
ment a I
ditnumber det T t
nu per day.. 0
per dao s a .
Calorie.s. Gin.. Gins. G(ni7. Gmis. Guus. Gm. Gmis. GOm. Gns. Gm.ns. Gas. Gam.
S......... 2,908 15.8? 0.74 14.31 +0.77 1.12 0.06 0.95 +0.11 2.29 0.78 1.41 -10.10
2....__.... 2,901 15.r2 .67 14.67 + .48 1.12 .03 .97 + .09 2.29 .73 1.48 + .08
3---------- 2,913 15.82 70 14.16 + .96 1.12 .06 .93 + .13 2.29 .78 1.42 + .09
4......2,0,o2 12.05 .74 10.43 + .81 .94 03 .72 + .13 1.40 .44 1.08 .07
5.-----..- 2,607 18.52 .87 16.50 +1.15 1.44 .08 1.1, + .24 3.07 1.10 1.74 + .28
(-.-......- 1,555 9.76 .27 10.94 -1.45 .69 .02 75 08 1.60 .37 1.12 + .11
..... 1,660 10.11 .45 11.51 -1.85 .70 .04 .17 1.58 .60 1.00 .02
8.......... 3,336 20. 22 1.04 15.52 +3.66 1.40 .09 1. + .25 8.16 1.42 1.49 + .25
9--.._-._. 1,656 10.11 .43 12.87 -3.19 .70 .04 .88 .22 1.58 50 1.32 .A
10----------. 3,329 20.70 1.05 16.58 +3.07 1.36 .10 1.21 + 05 3.26 1.37 1.49 + .40
The first three experiments show apparent daily gains of one-half to
1 gram of nitrogen and about one-tenth gram of sulphur and phos-
phorus. These apparent gains may be largely due to the undetermined
losses of urea, ammonium salts, sulphates and phosphates through
the skin, and of volatile compounds of nitrogen and sulphur through
the intestines. In experiment No. 5, in addition to the sources.of error
just mentioned, we have the effects of "lag" continuing through the
experiment, as explained above. Experiment No. 6 shows a moderate
loss of nitrogen and a corresponding loss of sulphur, but a slight :;
apparent gain of phosphorus. In this case, however, the elimination-
of phosphorus (as also of nitrogen and sulphur) by the intestine is
relatively so small as to mark the experiment as somewhat exceptional. ;
It may be said that in these six experiments the sulphur balance .
follows that of nitrogen, but in no case is the gain or loss great enough::"'
to justify calculations of the composition of the material stored ior e
broken down. .
WE i .:: .
In experiments Nos. 7, 8, and 91 the gains and losses are larger, and
S here it is probably safe to draw inferences regarding the composition
of the material stored or lost by the body, though the undetermined
errors already discussed will of course affect the accuracy of such
deductions. Neglecting these errors, the figures given for "balance"
would indicate that in the material lost in the first of these experi-
ments the ratio of sulphur to nitrogen was as 1:10.9, in that stored in
the second as 1:14.6, and in that lost in the third as 1:14. The ratio
in the food consumed was 1:14.4, in the food material actually absorbed
S(food minus feces) it was 1:14.6. It was calculated above that this
ratio in serum globulin is 1:14.3, in myosin 1:13.1, in serum albumin
1:7.1, and in the glycoproteids of connective tissue and of bone as
about 1:5. Thus the ratio is narrower in the tissue proteids gener-
ally than in the food here consumed, but in serum globulin the ratio
is about the same, and in myosin not greatly different. A strict inter-
:pretation of these ratios would thus lead to the conclusion that in the
S"fi rst period the body metabolized the food eaten and some of its own
material in which the ratio is narrower; that in the second, a part of
the protein of the food is either stored without essential change or con-
verted for storage into some form of body protein in which the ratio is
.....practically the same (as in the case with serum globulin), and that
the proteid lost in the third period was of the same nature as that
stored in the second period. Such a method of interpretation is in line
Switch that followed by Kolpatcka in his studies upon dogs, but for the
m reasons already given it is believed that such conclusions must be
accepted with reserve until more is known of the conditions influencing
S.the "balance" and the "lag." These experiments, however, do at
any rate strongly emphasize the close parallelism between the meta-
bolism of nitrogen and that of sulphur when the diet is normal and is
continued uniform for a period long enough to practically eliminate
the effects of the lag. In experiment No. 10, which continued but three
days, the balance is much influenced by the lag, so that in this case
the apparent gains show no relation to the proportions of the two
elements in the food.
On the other hand the phosphorus metabolism does not show such a
close parallelism to the metabolism of nitrogen. In experiment No. 7,
where the loss of nitrogen was nearly constant throughout, there was
at first a slight gain and later a slight loss of phosphorus, the net
result being an almost perfect balance. This is probably due to the
-omparative richness of the diet in phosphorus, so that it supplied
sufficient of this element for the needs of the body, while the protein
of. the diet was so far insufficient as to result in considerable loss of
: nitrogen and sulphur. During the five days of abundant diet (experi-
..Jment No. 8) there was a storage of 1.25 grams of phosphorus, and
f. almost exactly the same amount, was given up during the following
ive days of restricted diet. The three days of experiment No. 10
show a large apparent gain of phosphorus, but this is largely due to
the lag" and can not be considered to represent permanently-stored
Any comparison of the nitrogen and phosphorus metabolism in the
human organism is complicated by the varying proportions of phos-
phorus eliminated in the feces. Thus in experiments Nos. 8 and 9 the
diet was qualitatively the same, yet in the former 44.9 per cent and in
the latter only 31.6 per cent of the phosphorus in the food was found in
the feces. Two explanations suggest themselves, (1) that only a part
of the phosphates from body katabolism may appear in the urine, the
remainder being eliminated through the intestine, as in the herbivo-
rous animals; (2) that the proportion which the body absorbs may
depend not only upon the nature of the ingested phosphates, but also
upon the condition and needs of the body. The former is probably
true to some extent, but it seems probable that the latter also oper-
ates in some cases, as in that just mentioned, where, on doubling the
diet, a much smaller proportion of the phosphorus present was assim-
The larger proportion of ingested phosphorus which appears in the
feces makes the proper separation of the latter a much more impor-
tant matter in experiments in which the balance of phosphorus is to be
determined than in those in which only nitrogen or nitrogen and
sulphur are studied.
In view of the results which have recently been obtained upon the
assimilation of the phosphorus of casein,a the phosphates found in
the feces in these experiments should probably be attributed mainly
to the calcium phosphate of the food. It should be remembered also
that in the present experiments the diet was unusually rich in phos-
phates, and the proper interpretation of the results must await the
completion of similar experiments upon different diets.
The experiments here reported afford no data for a direct compari-
son of the nutritive values of different proteids, the food materials
used having been similar through the whole series. However, in view
of the recent work upon the nutritive value of the proteids of milk,6
it is interesting to note the tendency shown in experiments Nos. 1 to
4 to store protein on a diet considerably smaller than that usually
estimated for a subject of vigorous appetite and doing a considerable
amount of work.
a Marcuse, Arch.Physiol. .[Pfliiger], 67 (1897), p. 373; Knopfelmacher, Wiener
Klin. Wchnschr., 12 (1899), p. 1308; Nicko. Ztschr. Biol., 89 (1900), p. 430;
Miller, Ibid., p. 451.
bAmong the many recent papers may be noted: Marcuse, Arch. Physiol.
[Pfliiger], 64 (1896), p. 223; Steinitz, Ibid., 721 (1898). p. 75; Rohmann, Berl. Klin.
Wchnschr., 35 (1898), p. 789; Albu, Fortschr. Med., 17 (1899), p. 505; Poda and
Prausnitz, Ztschr. Biol., 39 (1899-1900), p. 279.
"".... ::: .::" '; ..:
The digestibility of the protein of the bread and milk diet as found
in nine of the ten experiments agreed closely with the results calcu-
lated, assuming 07 per cent as the coefficient for milk and 90 per cent
as that for bread. The digestibility was not appreciably influenced
Si:by loss of sleep nor by the continuance of the diet for twelve or
I: The proportions of protein digested from a restricted diet were
: about 0.7 per ceiit higher than those digested from a liberal diet of
Sthe same composition.
i Marked loss of sleep for three successive nights resulted in a small
Increase in the amounts of nitrogen, sulphur, and phosphorus excreted.
The increase of sulphur was proportional to that of nitrogen and the
III increase of phosphorus was very slightly larger, the relative difference
il being no greater than might be attributed to the usual daily varia-
The increased elimination resulting from loss of sleep did not appear
i: until the third day, while changes resulting from alteration of the diet
were always perceptible on the first day.
The data collected regarding the relative "lag" of nitrogen, sul-
phur, and phosphorus are not yet sufficient to permit general conclu-
'sions to be drawn.
In general the metabolism and "balance" of sulphur ran approxi-
mately parallel with that of nitrogen.
The renal elimination and "balance" of phosphorus showed fluctu-
ations similar to those of nitrogen, but not so closely parallel as in
the case of sulphur. The elimination of phosphorus by the intestine
was large and variable, making the accurate separation of the feces
an important factor in the determination of the phosphorus balance.
The above statements are intended merely to summarize the results
of the experiments here reported. As these were all made upon a
single subject and with only two or three food materials, it would obvi-
l. ously be unsafe to generalize broadly from the results. As already
explained, the work was undertaken not so much with a view to obtain-
ing results of intrinsic interest as to get data regarding methods of
work and possible sources of error, and thus facilitate the study of the
sulphur and phosphorus metabolism in connection with certain of the
series of nutrition investigations to which the present experiments
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