384 OF KESPIRATION. 



with the general development of the body, and also with the sex and 

 age, is considerable. Thus, the exhalation is almost always greater in 

 males, than in females of the same age, at every period of life except 

 childhood. In males, the quantity increases regularly from eight to 

 thirty years of age, remaining nearly stationary until forty ; thus it 

 averages 77*5 grains of carbon per hour at eight years; 135 grains at 

 fifteen ; 176'7 grains at twenty ; and 189 grains from thirty to forty. 

 Between forty and fifty, there is a well-marked diminution, the average 

 being then 156 grains ; and the diminution continues up to extreme old 

 age, when the amount exhaled scarcely exceeds that which is extricated 

 at ten years of age ; thus, between sixty and eighty, it was 142-5 

 grains; and in a man of a hundred and two, it was only 91*5 grains. 

 These average results, however, are widely departed from in individual 

 cases ; an extraordinary development of the muscular system being al- 

 ways accompanied by a high rate of extrication of carbon ; and vice 

 versd. Thus a man of remarkable muscular vigour, whose age was 

 twenty-six years, exhaled 217 grains of carbon in an hour ; a robust 

 man of sixty exhaled 209*4 grains; and an old man of ninety-two, who 

 in his younger days had possessed uncommon muscular power, and who 

 preserved a remarkable degree of energy, still gave forth at the rate of 

 151 grains per hour. On the other hand, a man of slight muscular 

 development, at the age of forty-five, only exhaled 132 grains ; and an- 

 other at the age of seventy-six, only 92-4 grains. 



693. In females, nearly the same proportional increase goes on, up 

 to the time of puberty ; when the quantity abruptly ceases to increase, 

 and remains stationary so long as menstruation continues regular. The 

 average quantity of carbonic acid exhaled by girls nearly approaching 

 puberty, is about 100 grains per hour ; and it remains at this standard 

 until nearly the close of menstrual life. At the period of the cessation 

 of the catamenia, it undergoes a perceptible increase ; the average be- 

 tween forty and fifty years of age, being about 130 grains per hour ; 

 and the quantity exhaled in a woman of great muscular development, 

 and of forty-four years of age, rising to 152-4 grains in an hour. After 

 the age of fifty, or thereabouts, the quantity decreases, as in men. It is 

 remarkable that, during pregnancy, there is the same increase in the 

 exhalation of carbon, as there is after the final cessation of the cata- 

 menia ; and the same takes place, if the menstrual discharge be tem- 

 porarily suspended, through any other cause. 



694. It is obviously difficult, then, to obtain exact estimates, from 

 any experiments conducted for a short time only, of the total amount 

 of Carbon thrown off during a lengthened period ; since the condition 

 of the individual varies so greatly at different times ; and the variation 

 amongst different individuals is so great. Moreover, of the total amount 

 of carbon excreted in a gaseous form, a certain part is undoubtedly set 

 free from the skin ; but the proportion of this does not seem to be con- 

 siderable. As a means of measuring the whole quantity of carbonic 

 acid set free, without causing the respiratory movements to be per- 

 formed in any unnatural manner, Prof. Scharling constructed an air- 

 tight chamber, of dimensions sufficient to allow an individual to remain 

 in it for some time without inconvenience ; and so arranged, that he 



