CONDITIONS INFLUENCING THE EXCRETION OF C0 2 . 



257 



The absolute amount of C0 2 given off is less in children than in adults; 

 but if the C0 2 given off be calculated with reference to body-weight, 

 then, weight for weight, a child gives off twice as much C0 2 as an adult. 



2. Sex. Males, from the eighth year onwards to old age, give off 

 about one-third more C0 2 than females (Andral and Gavarret). This 

 difference is more marked at puberty, when the difference may rise to 

 one-half. After cessation of the menses, there is an increase, and in old 

 age the amount of C0 2 given off diminishes. Pregnancy increases the 

 amount, owing to causes which are easily understood. 



3. The Constitution. As a general rule, muscular, energetic persons 

 use more and excrete more C0 2 than less active persons of the same 

 weight. 



4. Alternation of Day and Night. The C0 2 given off is diminished 

 during sleep about one-fourth (Scharling). This diminution is caused 

 by the constant heat of the surroundings (bed), darkness, absence of 

 muscular activity, and the non-taking of food (see 5, 6, 7, 9). It does 

 not seem that any is stored up during sleep (S. Lewin). After 

 awaking in the morning, the respirations are more rapid and deeper, 

 and thus the amount of C0 2 given off is increased. It decreases during 

 the forenoon, until dinner at mid-day causes another increase. It falls 

 during the afternoon, and increases again after supper. 



During hybernation, when no food is taken, and when the respirations 

 cease, or are enormously diminished, the respiratory exchange of gases 

 is carried out by diffusion and by the cardio-pneumatic movements 

 (p. 109). The C0 2 given off falls to T V, the taken in to ^ of what 

 they are in the waking condition (Valentin). Much less C0 2 is given 

 off than taken in, so that the body-weight may increase through the 

 excess of 0. 



5. Temperature of the Surroundings. Cold-blooded animals become 

 warmer when the temperature of their environment is raised, and they 

 give off more C0 2 in this condition than when they are cooler 

 (Spallanzani) e.g., a frog with the temperature of the surroundings at 



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