284 KESPIRATION. 



increases constantly with the age. Thus a boy of eight years exhales, 

 on the average, 9238 cubic centimetres per hour ; while a boy of fifteen 

 years exhales 16,168 cubic centimetres 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, 

 22,899 cubic centimetres 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 diminishes in a marked degree, 

 so that it may fall as low as IT, 000 cubic centimetres. In one superan- 

 nuated person, 102 years of age, Andral and Gavarret found the hourly 

 quantity of carbonic acid to be less than 11,000 cubic centimetres. 



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

 puberty; and its production then remains constant until the cessation 

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

 increases again until after fifty years, when it subsequently diminishes 

 with the approach of old age, as in men. Pregnancy, occurring at any 

 time in the above period, produces a temporary increase in the quantity 

 of carbonic acid. 



The strength of the constitution, and particularly the development of 

 the muscular system, was found to have a great influence in this respect. 

 The largest production of carbonic acid observed was in a young man, 

 26 years of age, whose frame presented a remarkably vigorous and 

 athletic development, and who exhaled 26,060 cubic centimetres per 

 hour. On the other hand, an unusually large skeleton, or an abundant 

 deposit of adipose tissue, is not accompanied by any similar increase of 

 the carbonic acid. 



Andral and Gavarret sum up the results of their investigation as 

 follows : 



1. The quantity of carbonic acid exhaled from the lungs in a given 

 time varies with the age, the sex, and the constitution of the subject. 



2. In the male, as well as in the female, the quantity of carbonic acid 

 varies according to age. 



3. During all periods of life, the male and female may be distinguished 

 by the different quantities of carbonic acid exhaled in a given time. 

 Other things being equal, the male exhales a larger quantity than the 

 female. This difference is particularly marked between the ages of 16 

 and 40 years, during which period the male usually exhales twice as 

 much carbonic acid as the female. 



4. In the male, the quantity of carbonic acid increases constantly from 

 eight to thirty years ; and the rate of this increase undergoes a rapid 

 augmentation at the period of puberty. Beyond forty years the exha- 

 lation of carbonic acid begins to decrease, and its diminution is more 

 marked as the individual approaches extreme old age, so that near the 

 termination of life, the quantity of carbonic acid produced may be no 

 greater than at the age of ten years. 



5. In the female, the exhalation of carbonic acid increases according 



