7 oo CHEMISTR Y OF RESPIRA TION. 
animal was placed ; this air was analysed for carbon dioxide, and the oxygen 
absorbed by the animal was replaced by a corresponding amount supplied from 
a gasometer. 
The consumption of oxygen by animals living in water can be determined 
by titrating a sample of the water before and after the confinement of the 
animal in a known volume of water. Quinquand 1 used for this purpose 
sodium hyp (sulphite, according to Schiitzenberger's method. 
The conditions which affect the respiratory exchange. — A de- 
termination of the respiratory exchange not only gives the absolute 
value of the oxygen absorbed, and of the carbon dioxide and water ex- 
creted, but also shows the relationship between the intake of oxygen 
and the output of carbon dioxide. This ratio between the volume of 
oxygen absorbed and the volume of carbon dioxide discharged is known as 
CO 
the respiratory quotient -~, and indicates how much of the oxygen com- 
2 
bines with carbon to form carbon dioxide, for one volume of oxygen in 
combining with carbon yields one volume of carbon dioxide. Various 
conditions influence both the amount of the respiratory exchange and 
the relative proportions of the gases, but it must be remembered that 
determinations of short duration may give rise to erroneous conclusions, 
for oxygen may be stored up for some time within the body, and 
carbon dioxide may still be formed and discharged when there is no 
intake of oxygen. 
The question here arises, Does nitrogen play any active part in 
respiration, is there any absorption or discharge of nitrogen ? 2 The 
older observers found that nitrogen was sometimes absorbed by the 
lungs, and in nearly all of Eegnault and Eeiset's 3 determinations of the 
respiratory exchange in different animals there is an alteration in the 
amount of nitrogen present in the air, denoting generally a discharge of 
a small quantity of nitrogen from the animal. Marchand 4 had also ob- 
tained similar results ; he found in ten experiments upon guinea-pigs 
that the average discharge of nitrogen was equal to 094 per cent, of the 
output of carbon dioxide, and in three experiments on pigeons to - 85 
per cent. Seegen and Xowak 5 also found a discharge of nitrogen, 
varying from 4 to 9 mgrms. per kilo, and hour in thirty-two experiments 
upon rabbits, dogs, and hens. 
This discharge of nitrogen in many cases appears to be due to an 
error of experiment. 6 Analyses, purposely made by Colasanti 7 to test 
this point, showed no discharge or absorption of nitrogen by guinea-pigs. 
The small amount observed by other experimenters may be due either 
to nitrogen discharged from the alimentary canal or to experimental 
errors. According to Jolyet, Bergonie, and Sigalas, 8 an amount of 
nitrogen varying from y^- to 10 8 00 of the oxygen absorbed is taken 
up by the blood in its passage through the lungs of a man or a dog. 
In any case the amount of nitrogen absorbed or discharged under 
1 Compt. rend. Acad. d. sc, Paris, 1S73, tome lxxvi. p. 1 J 41 . 
2 For further details, see Voit, Hermann's "Handbuch," Bd. vi., Th. 1, S. 37. 
3 Ann. dc chirm,, ct phys, Paris, 1849, Ser. 3, tome xxvi. 
4 Journ.f. pralct. Chem., Leipzig, 1848, Bd. xliv. S. 1. 
5 S'ifzungsb. d. I: Akad. d. Wissensch. Math.-naturw. CI., Wien, 1875. Bd. lxxi. (3), 
S. 329 ; Arch. f. d. ges. Physio/.. Bonn, 1879, Bd. xix. S. 347. 
6 Pettenkofer and Voit, Ztschr. f. Biol., Miinchen, 1880, Bd. xvi. S. 50S. 
7 Arch. f. d. f/cs. Physiol., Bonn, 1877, Bd. xiv. S. 92. 
8 Compt. rend. Acad. d. sc, Paris, 1887, tome cv. p. 675. 
