CHAP. XXTX.] EXHALATION OF CARBONIC ACID. 407 



ti gated, and by no one more extensively or more accurately than 

 by Dr. Snow, who has, among other matters, turned his attention 

 to the amount of carbonic acid gas passing from the lungs under 

 their use. A small animal being placed in a jar, in which the air 

 could be circulated in connection with a receptacle containing solu- 

 tion of potash, for absorbing the carbonic acid, the quantity of this 

 gas expired during periods of half an hour, was estimated, when 

 the animal breathed firstly air, and afterwards air mixed with 

 certain quantities of the vapour of chloroform. The results were 

 such as the following : A dog, eight pounds in weight, exhaled in 

 air 10- 1 grains of carbonic acid gas; in air mingled with 36 grains 

 of chloroform vapour, only 4'8 grains. A half-grown cat expired 

 in air 5*7 grains of carbonic, acid gas; in air mingled with 20 

 grains of chloroform vapour, only 2*0 grains. And this diminution 

 was observed, on this and other occasions, to be in spite of increased 

 muscular efforts on the first introduction of the chloroform, such as 

 are known to have a tendency to augment the excretion of carbonic 

 acid. 



Exercise increases the exhalation of carbonic acid, and doubtless 

 also the formation of it in the tissues. Mr. Newport observed that 

 the generation of carbonic acid from bees, when at rest, did not 

 exceed that from cold-blooded animals, but when in active move- 

 ment it was more energetic than in any other animals ; and other 

 experimenters have produced analogous results. With more pre- 

 cision, and in the case of the human adult, Vierordt shows, that, 

 during moderate exercise, there is an average increase per minute 

 of 19 cubic inches in the expired air, and of 1 cubic inch in the 

 expired carbonic acid. 



The temperature of the surrounding medium was shown by Seguin 

 and Lavoisier to have an important influence on the exhalation of 

 carbonic acid, and their results were corroborated by those of 

 Crawford. Vierordt has recently examined this point also. In 

 numerous experiments upon himself at temperratures of which 

 the average was 47 Fahrenheit, he expired 18'25 cubic inches 

 of carbonic acid per minute; while at temperatures of which 

 the average was 67 Fahrenheit, he expired only 15 '72 cubic 

 inches in the same period. At the lower temperature, the number 

 of respirations was increased, [and more air was expired in the 

 proportion of 406 to 366, or^ about 10 to 9. Cold, therefore, 

 contrary to what might have been expected from its depressing 

 effects on the system, is attended with an augmented exhalation 

 of carbonic acid, and, as will be afterwards seen, with an increased 



