222 RESPIRATION. 



brief notice, because it affords evidence concerning either 

 the sources of carbonic acid exhaled, or the mode in which 

 it is separated from the blood. 



a. Influence of Age and Sex. According to Andral and 

 Gavarret the quantity of carbonic acid exhaled into the 

 air breathed by males, regularly increases from eight to 

 thirty years of age ; from thirty to forty it is stationary 

 or diminishes a little ; from forty to fifty the diminution is 

 greater ; and from fifty to extreme age it goes on diminish- 

 ing, till it scarcely exceeds the quantity exhaled at ten 

 years old. In females (in whom the quantity exhaled is 

 always less than in males of the same age) the same 

 regular increase in quantity goes on from the eighth year 

 to the age of puberty, when the quantity abruptly ceases 

 to increase, and remains stationary so long as they con- 

 tinue to menstruate. When, however, menstruation has 

 ceased, either in advancing years or in pregnancy, or 

 morbid amenorrhcea, the exhalation of carbonic acid again 

 augments ; but when menstruation ceases naturally, it 

 soon decreases again at the same rate that it does in old 

 men. 



J. Influence, of Respiratory Movements. According to 

 Yierordt, the more quickly the movements of respiration 

 are performed, the smaller is the proportionate quantity 

 of carbonic acid contained in each volume of the expired 

 air. Thus he found that, with six respirations per minute, 

 the quantity of expired carbonic acid was 5*528 per cent ; 

 with twelve respirations, 4*262 per cent. ; with twenty- 

 four, 3 '3 5 5 ; with forty-eight, 2-984 ; and with ninety-six, 

 2-662. Although, however, the proportionate quantity of 

 carbonic acid is thus diminished during frequent respira- 

 tion, yet the absolute amount exhaled into the air within 

 a given time is increased thereby, owing to the larger 

 quantity of air which is breathed in the time. This is the 

 case, whether the respiration be voluntarily accelerated, 

 or naturally increased in frequency, as it is after feeding, 



