RESPIRATION. 1 89 



however, the proportionate quantity of carbonic acid is thus diminished 

 during frequent respiration, yet the absolute amount exhaled into the 

 air within a given time is increased thereby, owing to the larger quan- 

 tity of air which is breathed in the time. The last half of a volume of 

 expired air contains more carbonic acid than the half first expired ; a 

 circumstance which is explained by the one portion of air coming from 

 the remote part of the lungs, where it has been in more immediate and 

 prolonged contact with the blood than the other has, which comes 

 chiefly from the larger bronchial tubes. 



c. External temperature. The observation made by Vierordt at vari- 

 ous temperatures between 38 F. and 75 F. (3.4-23.8 C.) show, for 

 warm-blooded animals, that within this range, every rise equal to 10 

 F., causes a diminution of about two cubic inches in the quantity of 

 carbonic acid exhaled per minute. 



d. Season of the Year. The season of the year, independently of 

 temperature, materially influences the respiratory phenomena; spring 

 being the season of the greatest, and autumn of the least activity of the 

 respiratory and other functions. (Edward Smith.) 



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

 acid given out by the lungs constitutes about 4.3 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. 



/. Hygrometric State of Atmosphere. The amount of carbonic acid 

 exhaled is considerably influenced by the degree of moisture of the 

 atmosphere, much more being given off when the air is moist than when 

 it is dry. (Lehmann.) 



ff. Period of the Day. During the day-time more carbonic acid is 

 exhaled than corresponds to the oxygen absorbed; while, on the other 

 hand, at night very much more oxygen is absorbed than is exhaled in 

 carbonic acid. There is, thus, a reserve fund of oxygen absorbed by 

 night to meet the requirements of the day. If the total quantity of 

 carbonic acid exhaled in 24 hours be represented by 100, 52 parts are ex- 

 haled during the day, and 48 at night. While, similarly, 33 parts of the 

 oxygen are absorbed during the day, and the remaining 67 by night. 

 (Pette'nkofer and Voit.) 



h. Food and Drink. By the use of food the quantity is increased, 

 whilst by fasting it is diminished; it is greater when animals are fed on 

 farinaceous food than when fed on meat. The effects produced by 

 spirituous drinks depend much on the kind of drink taken. Pure alco- 

 hol tends rather to increase than to lessen respiratory changes, and the 

 amount therefore of carbonic acid expired; rum, ale, and porter, also 

 sherry, have very similar effects. On the other hand, brandy, whiskey, 

 and gin, particularly the latter, almost always lessened the respiratory 

 changes, and consequently the amount of carbonic acid exhaled. (Ed- 

 ward Smith.) 



i. Exercise. Bodily exercise, in moderation, increases the quantity 

 to about one-third more than it is during rest: and for about an hour 

 after exercise the volume of the air expired in the minute is increased 

 about 118 cubic inches: and the quantity of carbonic acid about 7.8 cubic 

 inches per minute. Violent exercise, such as full labor on the tread - 

 wheel, still further increases the amount of the acid exhaled. (Edward. 

 Smith.) 



