4:24 RESPIRATION. 



Yalentin had previously made experiments on this point, 

 and put the temperature of the expired air a little higher, 

 i. e., about 99, with an external temperature of 68. He 

 also showed that the temperature of the surrounding atmos- 

 phere exerted an important influence on the temperature of 

 the expired air. In. an observation made in winter, with an 

 external temperature of 18, the temperature of the expired 

 air was only 85 '5 . 1 



Exhalation of Carbonic Acid. The production of car- 

 bonic acid in the respiratory process is as universal as the 

 consumption of oxygen. Experiments have shown that all 

 animals during life exhale this principle, as well as all tis- 

 sues, so long as they retain their irritability. This takes 

 place, not only when the animals or tissues are placed in an 

 atmosphere of oxygen, or common air, but, as was observed 

 by Spallanzani, 2 in an atmosphere of pure nitrogen or hydro- 

 gen. This fact has since been noted by W. F. Edwards, J. 

 Miiller, G. Liebig, and others. 



The study of the exhalation of carbonic acid presents sev- 

 eral problems of great physiological interest : 



1. "What is the absolute quantity of carbonic acid exhaled 

 by the lungs in a given time ? 



2. What are the variations in the exhalation of this prin- 

 ciple due to physiological influences ? 



3. What is the relation between the quantity of carbonic 

 acid produced and the quantity of oxygen consumed ? 



On account of the variations in the quantities of carbonic 

 acid exhaled at different periods of the day, and particularly 

 the great influence of the rapidity of the respiratory move- 

 ments, it is exceedingly difficult to fix upon any number 

 which will represent the average proportion of this gas con- 

 tained in the expired air. The same influences were found 

 affecting the consumption of oxygen ; and the same difficulties 



1 GREHANT, Rtcherches Physiques sur la ^Respiration de VHomme. Journal de 

 V Anatomic d de la Physiologic, 1864, tome i., p. 545. 

 Op. cit., p. 343. 



