EFFECTS OF EXERCISE AND SLEEP. 177 



During sleep, on the other hand, there is a considerable 

 diminution in the quantity of this gas evolved ; a result, 

 probably, in great measure dependent on the tranquillity of 

 breathing ; directly after walking, there is a great, though 

 quickly transitory, increase in the amount exhaled. A larger 

 quantity is exhaled when the barometer is low than when it 

 is high. 



3. The Oxygen in Respired Air is always less than in the 

 same air before respiration, and its diminution is generally 

 proportionate to the increase of the carbonic acid. The ex- 

 periments of Valentin and Brunner seem to show that for 

 every volume of carbonic acid exhaled into the air, 1.17421 

 volumes of oxygen are absorbed from it ; and that when the 

 average quantity of carbonic acid, i. e., 1346 cubic inches, or 

 636 grains, is exhaled in the hour, the quantity of oxygen ab- 

 sorbed in the same time 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 without 

 change of volume ; and to this general conclusion, namely, 

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

 that of the air inspired (allowance being made for the expan- 

 sion 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 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 combining with sulphur and 

 phosphorus to form part of the acids of the sulphates and 

 phosphates excreted in the urine, and probably also, from the 

 experiments of Dr. Bence Jones, with the nitrogen of the de- 

 composing nitrogenous tissues. 



The quantity of oxygen consumed seems to vary much, not 

 only in different individuals, but in the same individual at 

 different periods ; thus it is considerably influenced by food, 

 being greater in dogs when fed on farinaceous than on animal 

 food, and much diminished during fasting, while it varies at 

 different stages of digestion. Animals of small size consume 

 a relatively much greater amoujit of oxygen than larger ones. 

 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 (Regnault and Reiset). 



The Nitrogen of the Atmosphere, in relation to the respira- 



