4:08 RESPIRATION. [CHAP. XXIX. 



development of animal heat. Of course there must be limits to this 

 result. 



MM. Andral and Gavarret have arrived at some remarkable 

 results regarding the influence of sex and age on the exhalation of 

 carbonic acid. They found that after the age of eight years, the 

 male exhales much more than the female, the average quantity 

 between the ages of 16 and 40 being double in the male. With 

 respect to each sex at different ages, the male child between 8 and 

 15 exhales per hour, in the form of carbonic acid gas, 77 grains of 

 carbon; the female about 15 grains less. In the male, the quantity 

 increases rather suddenly at puberty to 157 grains, and continues 

 increasing up to 25, when it averages 191 grains per hour (or 9J 

 ounces per day). It remains about stationary up to 40 years of 

 age ; between 40 and 60, it averages only 155 grains ; and between 

 60 and 80, 141 grains per hour. In one man of 102, remarkably 

 hale, it was only 91 grains ; in another of 26, remarkably fine 

 and muscular, it reached 217 grains. In the female, no great or 

 corresponding increase takes place at puberty; and as long as 

 menstruation is regular, the average exhalation of carbon is only 

 98 grains per hour. During pregnancy, however, and also at the 

 period of the cessation of the menses, it is singular to observe that 

 this quantity is quickly raised to 129 grains. Between 50 and 60, 

 the average is 112 grains; between 60 and 80, 104 grains. In a 

 woman of 82 it was only 92 grains per hour. Scharling has to 

 some extent corroborated these results. 



This increase in the male during the period of the greatest 

 activity and muscular vigour, and also the general higher standard 

 in the male, and the decline in both sexes with age, is accordant 

 with what we know of the rate and activity of the changes of 

 nutrition under these several conditions. The varieties in the 

 female are less easily explained, though obviously of great impor- 

 tance. It may be here remarked, that Hutchinson and Bourgery 

 have ascertained that the quantity of air breathed increases up to 

 30 or 35 years of age, then decreases slowly 65, and very much 

 in old age ; and also that it is less in females. 



Such are some natural circumstances modifying the quantity of 

 carbonic acid exhaled. The following conclusions of Vierordt on 

 the influence of the respiratory movements on the amount expired 

 are interesting in themselves, and throw light on the theory of 

 the respiratory function. He finds, that when the respirations are 

 increased in frequency, more carbonic acid is exhaled, although 

 from the much larger quantity of air breathed, the per centage of 



