AMOUNT OF CAKbONT DIOXIDE LXCU171KD 265 



Respiratory Movements. The quicker the respirations, the smaller is the percentage 

 of carbon dioxide contained in each volume of the expired air. Although the propor- 

 tionate quantity of carbon dioxide is thus diminished, tne absolute amount exhaled 

 within a given time is increased thereby, owing to the larger quantity 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 later 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 first portion exhaled has, which comes 

 chiefly from the larger bronchial tubes. 



External Temperature. The observation made by Vierordt at various temperatures 

 between ^.4-2^.8 C. (38 F. and 75 F.) show, for warm-blooded animals, that within 

 this range every rise equal to 5.5 C. (10 F.) causes a diminution of about 33 c.c. (2 

 cubic inches) in the quantity of carbon dioxide exhaled per minute. 



Season of the Year. The season of the year, independently of temperature, materi- 

 ally influences the respiratory phenomena since it influences the metabolism of the body; 

 spring being the season of the greatest, and autumn of the least, activity of the respira- 

 tory and metabolic functions. 



Purity of the Respired A ir. The average quantity of carbon dioxide given out by the 

 lungs constitutes about 4.38 per cent of the expired air; but if the air which is breathed 

 be previously impregnated with carbon dioxide (as is the case when the same air is fre- 

 quently respired), then the quantity of carbon dioxide exhaled becomes relatively much 

 greater. 



Hygrometric State oj the Atmosphere. The amount of carbon dioxide exhaled is con- 

 siderably influenced ty the degree of moisture of the atmosphere, much more being given 

 off when the air is moist than when it is dry. 



Period of the Day. The respiratory quotient, i.e., the ratio between carbon dioxide 

 eliminated and oxygen absorbed, is greater during the day than during the night. In 

 the day, therefore, the COa exhaled in relation to the O 2 absorbed is increased, and it 

 is diminished during the night. This is probably due to the increased production of 

 COa as a result of increased tissue activity during the day, and, consequently, the 

 breaking down or catabolism of more substances. 



Food and Drink. By the use of food the quantity of CO 2 is increased, while by fast 

 ing it is diminished; it is greater when animals are fed on farinaceous food than wheif 

 fed on meat. The effects produced by spirituous drinks depend much on the kind ot 

 drink taken. Pure alcohol in very small amounts tends rather to increase than to lessen 

 respiratory changes, and the amount, therefore, of carbon dioxide expired. Rum, ale, and 

 porter, also sherry, have very similar effects. On the other hand, brandy, whisky, and 

 gin in greater amounts almost always lessen the respiratory changes, and, consequently, 

 the amount of the gas exhaled. This is primarily due to their influence on the rate of 

 metabolism in each instance. 



Exercise. Bodily exercise, in moderation, increases the quantity of CO 2 expired by at 

 least one-third more than it is during rest. For about an hour after exercise the volume 

 of the air expired in the minute is increased nearly 2,000 c.c., or 118 cubic inches; and the 

 quantity of carbon dioxide about 125 c.c., or 7.8 cubic inches per minute. Violent exercise, 

 such as full labor or athletic competition, still further increases the amount of the carbonic 

 acid exhaled. 



The Oxygen is Diminished. Pettenkofer and Voit have found that the 

 mean consumption of oxygen during 24 hours, by a man weighing 70 kilos, 

 is about 700 grams or 490 liters. The quantity of oxygen absorbed increases 

 with muscular exercise, and falls during rest. In general terms the quantity 

 absorbed varies with the activity of the metabolic processes, following very 

 closely the variation of carbon dioxide under the conditions outlined above. 



The Volume of the Respired Air is Diminished. When allowance has 

 been made for the expansion in heating, the volume of expired air is decreased. 



