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AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



grams of CO 2 given off per kilogram of body-weight per hour : Goose, 1 .49 ; 

 fowl, 1.66; duck, 2.27; pigeon, 3.36; and finch, 12.58. 



In the same species, other things being equal, the respiratory interchange is 

 greater in smaller animals, because in relation to body-weight the body-surface 

 is greater, causing a greater proportional heat-loss, which in turn necessitates a 

 larger consumption of O for oxidative processes to produce heat, and a conse- 

 quent increase in the production of CO 2 . Richet l has shown that in the same 

 species the quantity of CO 2 exhaled (indicating the intensity of the oxidation- 

 processes) is inversely proportional to the body- weight and is directly propor- 

 tional to the body-surface. The following figures illustrate these important 

 facts: 



Thus, au animal weighing 24 kilograms will give off 1.026 grams of CO 2 

 per hour for each kilogram of body-weight, while one weighing 3.1 kilograms 

 will give off 1.964 grams, or nearly twice as much, for equal increments of 

 weight. It will be observed by comparing the quantity of CO 2 and the body- 

 surface that for each 100 square centimeters of surface the elimination is about 

 the same. 



Age exercises an important influence. Until full growth respiratory activity 

 is higher than in middle life, and in middle life it is higher than in old age. 

 In children the absolute quantities of O consumed and CO 2 formed are less 

 than in the adult, but in relation to body-weight they are about twice as much. 

 During middle life respiratory activity is about one-sixth higher than during 

 old age. In the young the quantity of O in relation to CO 2 is higher than in 

 the adult. 



Andral and Gavarret have shown, in investigations relative to sex, that 

 after the eighth year males give off from one-third to one-half more CO 2 than 

 females, the difference being most pronounced at puberty. During pregnancy 

 and after the menopause the relative quantity of CO 2 rises. 



The influence of constitution is manifest by a greater intensity of respi- 

 ratory activity in the robust than in the weak, other conditions being the 

 same. 



The rate and depth of the respiratory movements do not appreciably affect 

 the volumes of O and CO 2 interchanged, although the removal of CO 2 is facili- 

 tated by an increase of the volume of air respired, because of the better ven- 

 tilation of the lungs. Au increase in the rate, the depth remaining constant, 

 increases the volume of air respired and the absolute quantity of CO 2 given 

 off, but the quantity of CO 2 in relation to the total volume of air is less. If 



1 Archw de Physiologic normale et pathologique, vol. 22, pp. 17-30. 



