RESPIRATION. 195 



For every volume of carbonic acid exhaled into the air, 1 -17421 volumes 

 of oxygen are absorbed from it, and 1346 cubic inches, or 636 grains, be- 

 ing exhaled in the hour, the quantity of oxygen absorbed in the same tirrte 

 is 1584 cubic inches, or 542 grains. According to this estimate, there is 

 more oxygen absorbed than is exhaled with carbon to form carbonic acid. 



4. The volume of air expired in a given time is less than that of the 

 air inspired (allowance being made for the expansion in being heated), 

 niul that the loss is due to a portion of oxygen absorbed and not returned 

 in the exhaled carbonic acid, all observers agree, though as to the actual 

 quantity of oxygen so absorbed, they differ even widely. The amount of 

 oxygen absorbed is on an average 4 -8 per cent., so that the expired air 

 contains l(j'2 volumes per cent, of that gas. 



The quantity of oxygen that does not combine with the carbon given 

 off in carbonic acid from the lungs is probably disposed of in forming 

 some of the carbonic acid and water given off from the skin, and in com- 

 bining with sulphur and phosphorus to form part of the acids of the sul- 

 phates and phosphates excreted in the urine, and probably also, with the 

 nitrogen of the decomposing nitrogenous tissues. (Bence Jones.) 



The quantity of oxygen in the atmosphere surrounding animals, ap- 

 pears to have very little influence on the amount of this gas absorbed by 

 them, for the quantity consumed is not greater even though an excess of 

 oxygen be added to the atmosphere experimented with. 



It has often been discussed whether Nitrogen is absorbed by or exhaled 

 from the lungs during respiration. At present, all that can be said on 

 the subject is that, under most circumstances, animals appear to expire 

 a very small quantity above that which exhts in the inspired air. During 

 prolonged fasting, on the contrary, a small quantity appears to be ab- 

 sorbed. 



5. The watery vapor is increased. The quantity emitted is, as a gen- 

 eral rule, sufficient to saturate the expired air, or very nearly so. Its abso- 

 lute amount is, therefore, influenced by the following circumstances, (1), 

 by the quantity of air respired; for the greater this is, the greater also 

 will be the quantity of moisture exhaled. (2), by the quantity of watery 

 vapor contained in the air previous to its being inspired; because the 

 greater this is, the less will be the amount required to complete the satu- 

 ration of the air; (3), by the temperature of the expired air; for the 

 higher this is, the greater will be the quantity of watery vapor required 

 to saturate the air; (4), by the length of time which each volume of in- 

 spired air is allowed to remain in the lungs; for although, during ordinary 

 respiration, the expired air is always saturated with watery vapor, yet 

 when respiration is performed very rapidly the air has scarcely time to be 

 raised to the highest temperature, or be fully charged with moisture ere 

 it is expelled. 



