212 RESPIRATION. 



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. 



b. Influence of Respiratory Movements. According to 

 Vierordt, 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*355 ; 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, 

 active exercise, etc. By diminishing the frequency, and 

 increasing the depth of respiration, the per -centage pro 

 portion of carbonic acid in the expired air is diminished ; 

 being in the deepest respiration as much as I '97 per cent, 

 less than in ordinary breathing. But for this proportionate 

 diminution also, there is a full compensation in the greater 

 total volume of air which is thus breathed. Finally, the 

 last half of a volume of expired air contains more carbonic 

 acid than the half first expired ; a circumstance which is 

 explained by the one portion of air coming from the 

 remote part of the lungs, where it has been in more 



