CHANGES IX THE BLOOD DURING RESPIRATION. 251 



diminishes with the approach of old age, as in men. Pregnancy, 

 occurring at any time in the above period, immediately produces a 

 temporary increase in the quantity of carbonic acid. 



The strength of the constitution, and more particularly the deve- 

 lopment of the muscular system, was found to have a very great in- 

 fluence in this respect ; increasing the quantity of carbonic acid 

 very much in proportion to the weight of the individual. 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 1591 cubic inches per hour. 

 This large quantity of carbonic acid, moreover, in well developed 

 persons, is not owing simply to the size of the entire body, but 

 particularly to the development of the muscular system, since an 

 unusually large skeleton, or an abundant deposit of adipose tissue, 

 is not accompanied by any such increase of the carbonic acid. 



Andral and Gavarret finally sum up the results of their investiga- 

 tions 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 the age ; and that independently of the 

 weight of the individual subjected to experiment. 



3. During all the periods of life, from that of eight years up to 

 the most advanced age, the male and female may be distinguished 

 by the different quantities of carbonic acid which they exhale in a 

 given time. Other things being equal, the male exhales always 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 thirty 

 years the exhalation 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 accord- 

 ing to the same law as in the male, from the age of eight years 

 until puberty. But at the period of puberty, at the same time with 

 the appearance of menstruation, the exhalation of carbonic acid, 



