7*4 
CHEMISTR Y OF RESPIRA TION. 
is almost immediate. The contrast in the case of young mice of 
different ages is shown by the fact that a fall in external tempera- 
ture produces a fall in the output of carbon dioxide, and in the 
temperature of the young mouse, until it is about nine days old, when 
it begins to respond in a similar way to that observed in a full-grown 
animal. 
A similar development can be observed in other young animals born 
in an immature condition, and in the chick x before and after it is 
hatched, but a marked contrast is found in young animals born with a 
well-developed and active body. 2 
The influence of muscular activity upon the respiratory ex- 
change. — Muscular activity greatly increases the rate of breathing, the 
intake of oxygen, and the output of carbon dioxide. It was but natural, 
therefore, that physiologists should attribute the hyperpnoea caused by 
excessive muscular exertion to a deficiency of oxygen, or to an accumula- 
tion of carbon dioxide in the blood, consequent upon the greatly increased 
metabolism. This theory, however, has been proved by experiment to 
be erroneous. Mathieu and Urbain 3 determined the gases present in 
samples of blood removed from an animal after a period of rest, and 
again after a period of activity, and they found as a general result an 
increase in the oxygen, and a decrease in the carbon dioxide of the 
blood in the latter condition. Their analyses, however, were subject to 
certain sources of error. The question has been more thoroughly 
investigated by Geppert and Zuntz, 4 who found that muscular activity 
is indeed accompanied by an increase in the oxygen and a decrease in 
the carbon dioxide of the blood, and that the hyperpnoea is probably due to 
some product of muscular activity w^hich is absorbed by the blood and 
carried to the medulla oblongata, where it stimulates the respiratory 
centre. The chief evidence for these statements will now be given. 
After section of the spinal cord of a dog in the dorsal region, tetanisation 
of the hind limbs causes an increase in the air inspired, in the intake of 
oxygen, and in the output of carbon dioxide. 5 
Dog iceighing 2100 Grms. 
Volume of Air inspired 
per Minute. 
Intake of Oxygen. 
Output of Carbon Dioxide. 
CO., 
°2 
Condition. 
1012 c.C. 
Per Kilo. Bod 
20-4 c.c. 
• Weight and per Minute. 
18-2 c.c. 
•89 
Rest. 
2148 „ 
36-8 „ 
31-8 ,, 
•86 
Tetanus. 
863 ,, 
21-6 „ 
16-2 ,, 
"75 
Rest. 
1326 ,, 
29-5 „ 
19-3 ,, 
■66 
Tetanus. 
1 Pembrey. Gordon, and Warren, Journ. Physiol., Cambridge and London, 1894-95, 
vol. xvii. p. 331. 
2 See also "Animal Heat," this Text-book, vol. i. p. 803. 
3 Arch, dc physiol. norm, et jjaM., Paris, 1871-72, tome iv. ; Compt. rend. Acad. d. sc, 
Paris, 1872, tome lxxiv. p. 190. 
4 Arch./, d. gcs. Physiol., Bonn, 1888, Bd. xlii. S. 189. 
5 See also Hanriot and Richet, Compt. rend. Acad. d. sc, Paris, 1888, p. 75. 
