INFLUENCE OF TEMPERATURE AND SEASON. 213 



immediate and prolonged contact with the blood than the 

 other has, which comes chiefly from the larger bronchial 

 tubes. 



c. Influence of external Temperature. The observations 

 made by Vierordt at various temperatures between 38 F. 

 and 75 F. show, for warm-blooded animals, that within 

 this range, every rise equal to IO F. causes a diminution 

 of about two cubic inches in the quantity of carbonic 

 acid exhaled per minute. Letellier, from experiments 

 performed on animals at much higher and lower tempera- 

 tures than the above, also found that the higher the tempe- 

 rature of the respired air (as far as 104 F.), the less is the 

 amount of carbonic aid exhaled into it, whilst the nearer 

 it approaches zero the more does the carbonic acid increase. 

 The greatest quantity exhaled at the lower temperatures he 

 found to be about twice as much as the smallest exhaled at 

 the higher temperatures. 



d. Season of the Year. Dr. Edward Smith has shown 

 that the season of the year, independently of temperature, 

 also materially influences the respiratory phenomena ; for 

 with the same temperature, at different seasons, there is a 

 great diversity in the amount of carbonic acid expired. 

 According to his observations, spring is the season of the 

 greatest, and autumn of the least activity of the respiratory 

 and other functions. 



e. Purity of the Respired Air. The average quantity of 

 carbonic acid given out by the lungs constitutes about 4*48 

 per cent, of the expired air ; but if the air which is breathed 

 be previously impregnated with carbonic acid (as is the case 

 when the same air is frequently respired), then the quantity 

 of carbonic acid exhaled becomes much less. This is 

 shown by the results of two experiments performed by 

 Allen and Pepys. In one, in which fresh air was taken in 

 at each respiration, thirty-two cubic inches of carbonic acid 

 were exhaled in a minute ; whilst in the other, in which the 

 same air was respired repeatedly, the quantity of carbonic 



