EXHALATION OF CARBONIC ACID. 147 



human subject. The principal conditions which influence the exhalation of this principle 

 are the following : Age and sex ; activity or repose of the digestive system ; form of 

 diet; sleep; muscular activity ; fatigue; moisture and surrounding temperature; season 

 of the year. 



Influence of Age. In treating of the consumption of oxygen, it was stated that, during 

 the first few days of extra-uterine existence, the demand for oxygen on the part of the 

 system is very slight. At this period there is a correspondingly-feeble exhalation of 

 carbonic acid. It is well known that, during the first hours and days after birth, the new 

 being has little power of generating heat, needs constant protection from changes in tem- 

 perature, and the voluntary movements are very imperfect. During the first few days, 

 indeed, the infant does little more than sleep and take the small quantity of colostrum 

 which is furnished by the mammary glands of the mother. While the animal functions 

 are so imperfectly developed and until the nourishment becomes more abundant and the 

 child begins to increase rapidly in weight, the quantity of carbonic acid exhaled is very 

 small. 



After the respiratory function has become fully established, it is probable, from the 

 greater number of respiratory movements in early life, that the production of carbonic 

 acid, in proportion to the weight of the body, is greater in infancy than in adult life. 

 Direct observations, however, are wanting on this point. 



The observations of Andral and Gavarret show the comparative exhalation of carbonic 

 acid in the male, from the age of twelve to eighty-two, and give the results of a single 

 observation at the age of one hundred and two years. They show an increase in the 

 absolute quantity exhaled, from the age of twelve to thirty-two; a slight diminution, 

 from thirty-two to sixty ; and a considerable diminution, from sixty to eighty-two. These 



results are given in the following table: 



Carbonic acid exhaled per hour 



In boys from twelve to sixteen years 915 cubic inches. 



In young men from seventeen to nineteen years 1,220 " " 



In men from twenty-five to thirty-two years. 1,343 " " 



In men from thirty-two to sixty years 1,220 " " 



In men from sixty-three to eighty-two years 933 " " 



In an old man of one hundred and two years 671 



Taking into consideration the increase in the weight of the body with age, it is evident 

 that the respiratory activity is' much greater in youth than in adult life. Andral and 

 Gavarret do not give the weight of the subjects of their observations, but, as the weight 

 generally does not diminish after maturity, there can be no doubt that there is a rapid 

 diminution in the relative quantity of carbonic acid produced in old age. 



Scharling, in a series of observations on a boy nine years of age and weighing 48-5 

 pounds, an adult of twenty-eight, and one of thirty-five years, the latter weighing 163'6 

 pounds, showed that the respiratory activity in the child was nearly twice as great, in 

 proportion to his weight, as the average in the adults. It is seen, from the observations 

 of Andral and Gavarret, that the absolute increase in the exhalation of carbonic acid from 

 childhood to adult life is very slight in comparison with the natural increase in the 

 weight of the body; showing that, proportionately, the exhalation of carbonic acid is 

 greater in early life. 



Influence of Sex. All observers have found a marked difference between the sexes, in 

 favor of the male, in the proportion of carbonic acid exhaled. Andral and Gavarret noted 

 an absolute difference of about forty-five cubic inches per hour but did not take into 

 consideration the differences in the weight of the body. Scharling, taking the proportion 

 exhaled to the weight of the body, noted a marked difference in favor of the male. 



The difference in the degree of muscular activity in the sexes is sufficient to account 

 for the greater evolution of carbonic acid in the male, for this principle is exhaled in pro- 

 portion to the muscular development of the individual ; but there is an important differ- 



