152 RESPIRATION 



sex the increase is said to cease at puberty and to remain con- 

 stant until the menopause, after which time it increases to sixty 

 and diminishes subsequently. 



During digestion the quantity is considerably increased. This 

 is probably due to the muscular activity of the alimentary tract, 

 to glandular metabolism and to changes taking place in the food 

 products. 



As to diet, it may be said in general that the exhaled CO 2 is 

 increased in quantity by the taking of nitrogenized foods, tea 

 and coffee. 



The influence of sleep is to diminish the output. 



Muscular exercise is very efficient in increasing the amount of 

 CO 2 exhaled; in fact, this explains partly the variations in con- 

 nection with sex, digestion, sleep, etc. 



A high degree of moisture increases the exhalation, as does 

 a rise in body temperature. A rise in external temperature, how- 

 ever, has an opposite effect. 



The output is increased in spring and decreased in autumn. 



When the efferent nerve supplying a part is severed the pro- 

 duction of CO 2 in that part is at once diminished. 



The consumption of O and the exhalation CO 2 bear a fairly 

 constant relation to each other any condition increasing one in- 

 creasing the other, and vice versa. The facts, therefore, which 

 have been mentioned as governing the exhalation of CO 2 may 

 be applied to the consumption of O. 



(c) Gain in Temperature. When the body temperature is 

 normal and the external atmospheric temperature aboutyo F., 

 it is found that air inspired through the nose and expired through 

 the mouth has its temperature raised from 70 to about 95; 

 the rise is less when inspiration takes place through the mouth. 

 The last air of expiration is warmer than the first. This gain 

 of heat while the air is in the lungs needs no explanation when 

 it is remembered that the average temperature of the tissues 

 with which it is in contact is 98.5 F., or higher. 



