194 HAND-BOOK OF PHYSIOLOGY. 



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 T. (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 res- 

 piratory 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 car- 

 bonic 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 atmos- 

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

 dry. (Lehmann.) 



g. Period of the Day. During the daytime more carbonic acid is ex- 

 haled 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 ex- 

 haled in 24 hours be represented by 100, 52 parts are exhaled during the 

 day, and 48 at night. While, similarly, 33 parts of the oxygen are ab- 

 sorbed during the day, and the remaining 67 by night. (Pettenkofer 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 spiritu- 

 ous drinks depend much on the kind of drink taken. Pure alcohol 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, whisky, and gin, par- 

 ticularly the latter, almost always lessened the respiratory changes, and 

 consequently the amount of carbonic' acid exhaled. (Edward 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.) 



A larger quantity is exhaled when the barometer is low than when it 

 is high. 



3. The oxygen is diminished, and its diminution is generally propor- 

 tionate to the increase of the carbonic acid. 



