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 1 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 which 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, tetamsation 

 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 weighing 2100 Grms. 



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. dephysiol. norm, ct path., Paris, 1871-72, tome iv. ; Compt. rend. Acad. d. sc. t 

 Paris, 1872, tome Ixxiv. p. 190. 



4 Arch.f. d. ges. Physiol., Bonn, 1888, Bd. xlii. S. 189. 



5 See also Hanriot and Richet, Compt. rend. Acad. d. sc., Paris, 1888, p. 75. 



