I NFL UENCF OF A CTLVLTY ON PR O TELD ME TABOLLSM. 9 1 1 
the body, but especially those with much lymphoid tissue. 1 In amphibia 
and tishes the oxidation to uric acid does not occur, and this substance is not 
found in the urine. 2 Part of the uric acid of the bird's urine appears to be 
produced in the same manner as in mammals, and does not disappear after 
extirpation of the liver. 3 
Influence of muscular activity on proteid metabolism. — As 
we have already insisted upon, the greater part of the metabolism of 
the body goes on in the muscles. This is the case both when at rest 
and in activity, but their metabolism is greatly increased during activity. 
This is sufficiently shown by the fact that a much larger amount of 
carbonic acid is given off from the body when the muscles are con- 
tracting actively than when in a condition of rest ; and the chemical 
changes which can be shown to occur in the muscles as a result of 
contraction, such as the production of sarcolactic acid and of C0 2 , as 
well as the disappearance of glycogen, must mean increased metabolism. 
Although there is a general consensus of opinion that the CO., output 
of the body is largely increased as a result of muscular activity, the evidence 
that the C0 2 leaves the muscles as such is by no means conclusive. The 
observations which have been made upon this subject are of two kinds, 
namely, (a) the observation of the C0 2 given off by excised "surviving" 
frog's muscle, tetanised at intervals, as compared with the amount given off by 
corresponding muscle at rest ; and (b) the observation of the amount of C0 2 in 
the venous blood of the muscles of mammals, taken during conditions of rest 
and of contraction of the muscles respectively. The best-known experiments 
of the first kind are those of L. Hermann, 4 in confirmation of the results of 
Matteuci 5 and Valentin, 6 who found that the C0 2 yielded by tetanised frog 
muscles was greater in amount than that yielded by resting muscles under like 
conditions. The difference, however, was greatly diminished by agitation of 
non-contracting muscles. A careful repetition of this experiment, conducted 
in 1893-4 in my laboratory, by L. Hill, 7 failed to show to the most careful 
analysis any appreciable difference in the C0 2 output of two such 
sets of muscles (contracting and resting). Similar experiments by Tissot 8 
yielded results confirmatory of those of Hermann. Recently the question 
has been again investigated by Fletcher, 9 who employed a titration method 
for the estimation of the CO.,, and made use of the extremely accurate ap- 
paratus devised by Blackman 10 for estimating the gaseous exchanges in plants. 
Fletcher, both with skeletal and • with cardiac muscle (tortoise), was able 
to obtain only the smallest possible difference of C0 2 output between rest 
and contraction, and he comes to the conclusion that the contrary 
results obtained by Hermann and others are due to the prolonged stimula- 
tion inducing the commencement of rigor mortis, a condition which is 
attended by a considerable output of C0 2 . The other method of investi- 
gation, by the estimation of the C0 2 contained in the blood which has 
passed through muscular tissue, as compared with that entering it, was 
first undertaken by Ludwig and Sczelkow u upon muscles in situ in the 
1 Horbaczewski, Monatsh. f. Chem., Wien, 1889, Bd. x. S. 624, and loc. cit., supra. 
2 Nebelthau, Ztschr. f Biol., Miinchen, 1889, Bd. xxv. S. 129. 
3 Minkowski, loc. cit. 
4 " Stoffwechsel der Muskeln," Berlin, 1867. 
5 Ann. de chim. etphys., Paris, 1856, Ser. 3, tome 47. 
6 Arch. f. pkysiol. Heilk., Stuttgart, 1857. 
7 Hitherto unpublished. 
8 Arch, dephysiol. norm, etpath., Paris, 1894-5. 
tf Communication to the Physiological Society, May 1897, not yet published. 
10 Phil. Trans., London, 1895, vol. clxxxvi. p. 485. 
11 Sitzungsb. d. k. ATcad. d. Wissensch., Wien, 1862, Bd. xlv. 
