EFFECTS OF EXEECISE AND SLEEP. 215 



therefore, of carbonic acid expired : rum, ale, and porter, 

 also sherry, had very similar effects. On the other hand, 

 brandy, whisky and gin, particularly the latter, almost 

 always lessened the respiratory changes, and consequently 

 the amount of carbonic acid exhaled. 



i. Exercise and Sleep. Bodily exercise, in moderation, in- 

 creases 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 1 1 8 

 cubic inches : and the quantity of carbonic acid about 7 '8 

 cubic inches per minute. Violent exercise, such as full 

 labour on the treadwheel, still further increases, according 

 to Dr. E. Smith, the amount of the acid exhaled. 



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

 diminution in the quantity of this gas evolved ; a result pro- 

 bably 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 

 experiments of Valentin and Brunner seem to show, that, 

 for every volume of carbonic acid exhaled into the air, 

 I '1742 1 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 absorbed in the same time is 1 5 84 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 expansion in being heated), and that 

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



