250 RESPIRATION. 



adult man gives off 1.62 cubic inch of carbonic acid with each nor- 

 mal expiration. This amounts to very nearly 1,150 cubic inches 

 per hour, or fifteen and a half cubic feet per day. This quantity 

 is, by weight, 10,740 grains, or a little over one pound and a half. 

 The amount of carbonic acid exhaled, however, varies from time to 

 time, according to many different circumstances ; so that no such 

 estimate can represent correctly its quantity at all times. These 

 variations have been very fully investigated by Andral and Gavar- 

 ret, 1 who found that the principal conditions modifying the amount 

 of this gas produced were age, sex, constitution and development. 

 The variations were very marked in different individuals, notwith- 

 standing that the experiments were made at the same period of the 

 day, and with the subject as nearly as possible in the same condi- 

 tion. Thus they found that the quantity of carbonic acid exhaled 

 per hour in five different individuals was as follows : 



QUANTITY OF CARBONIC ACID PER HOUR. 



In subject No. 1 1207 cubic inches. 



" " " 2 970 " " 



" " " 3 1250 " 



" " " 4 1250 " " 



" " 5 1591 " 



With regard to the difference produced by age, it was found that 

 from the period of eight years up to puberty the quantity of car- 

 bonic acid increases constantly with the age. Thus a boy of eight 

 years exhales, on the average, 564 cubic inches per hour ; while a 

 boy of fifteen years exhales 981 cubic inches in the same time. 

 Boys exhale during this period more carbonic acid than girls of the 

 same age. In males this augmentation of the quantity of carbonic 

 acid continues till the twenty-fifth or thirtieth year, when it reaches, 

 on the average, 1398 cubic inches per hour. Its quantity then 

 remains stationary for ten or fifteen years ; then diminishes slightly 

 from the fortieth to the sixtieth year ; and after sixty years dimi- 

 nishes in a marked degree, so that it may fall so low as 1038 cubic 

 inches. In one superannuated person, 102 years of age, Andral 

 and Gavarret found the hourly quantity of carbonic acid to be 

 only 665 cubic inches. 



In women, the increase of carbonic acid ceases at the period of 

 puberty ; and its production then remains constant until the cessa- 

 tion of menstruation, about the fortieth or forty-fifth year. At that 

 time it increases again until after fifty years, when it subsequently 



1 Annales de Chimie et de Thai-made, 1843, vol. viii. p. 129. 



