190 HANDBOOK OF PHYSIOLOGY. 



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. 



For every volume of carbonic acid exhaled into the air, 1.17421 

 volumes of oxygen are absorbed from it, and 1346 cubic inches, or 630 

 grains being exhaled in the hour the quantity of oxygen absorbed in the 

 same time is 1584 cubic inches or 542 grains. According to this esti- 

 mate, 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), 

 and 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 of 4.8 per cent, so that the expired 

 air contains 16.2 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 off in forming 

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

 combining with sulphur and phosphorus to form part of the acids of the 

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

 the nitrogen of the decomposing nitrogenous tissues. 



The quantity of oxygen in the atmosphere surrounding animals 

 appears 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 ex- 

 haled 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 exists in the inspired air. 

 During prolonged fasting, on the contrary, a small quantity appears to 

 be absorbed. 



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

 general rule, sufficient to saturate the expired air, or very nearly so. 

 Its absolute amount is, therefore, influenced by the following circum- 

 stances (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; be- 

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

 the saturation 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 re- 

 quired to saturate the air; (4) by the length of time which each volume of 



