214 RESPIRATION. 



acid emitted in the same time was only Q'5 cubic inches. 

 They found also that, however often the same air may be 

 respired, even if until it will no longer sustain life, it does 

 not become charged with more than ten per cent, of carbonic 

 acid. The necessity of a constant supply of fresh air, by 

 means of ventilation, through rooms in which many persons 

 are breathing together, or in which, from any other source, 

 much carbonic acid is evolved, is thus rendered obvious ; 

 for even when the air is not completely irrespirable, yet in 

 the same proportion as it is already charged with carbonic 

 acid, does the further extrication of that gas from the lungs 

 suffer hindrance. 



/. Hyyrometric State of Atmosphere. Lehmann's observa- 

 tions have shown that the amount of carbonic acid exhaled 

 is considerably influenced by the degree of moisture of the 

 atmosphere, much more being given off when the air is 

 moist than when it is dry. 



g. Period of the Day. The period of day seems to exercise 

 a slight influence on the amount of carbonic acid exhaled 

 in a given time, though beyond the fact that the quantity 

 exhaled is much less by night, we are scarcely yet in a posi- 

 tion to state that variations in the amount exhaled occur at 

 uniform periods of the day, independently of the influence 

 of other circumstances. 



h. Food. By the use of food the quantity is increased, 

 whilst by fasting it is diminished : and, according to Reg- 

 nault and Reiset, it is greater when animals are fed on fari- 

 naceous food than when fed on meat. Spirituous drinks, 

 especially when taken on an empty stomach, are generally 

 believed to produce an immediate and marked diminution 

 in the quantity of this gas exhaled. Recent observations 

 by Dr. Edward Smith, however, furnish some singular re- 

 sults on this subject. Dr. Smith found, for example, that 

 the effects produced by spirituous drinks depend much on 

 the kind of drink taken. Pure alcohol tended rather to 

 increase than to lessen respiratory changes, and the amount, 



