RESPIRATORY INTERCHANGE UNDER DIFFERENT CONDITIONS 515 



an oxygen requirement of only 0.07 per kilo of weight, which is from 6 to 18 times 

 smaller than that of different species of warm-blooded animals. When considered 

 in a relative way, it also holds true that the smaller animals display a more intense 

 respiratory interchange than the larger. This fact may readily be deduced from 

 the following compilation, containing the oxygen consumption for each kilo of 

 weight : in the horse 0.437, calf 0.48, sheep 0.499, ox 0.55, rabbit 0.92, and cat 1.00. 

 This rule may also be applied to animals of the same species, because the body- 

 surface of the smaller ones is more extensive in relation to their body-weight than 

 that of the larger. This implies that the loss of heat is proportionately much greater 

 in the smaller animals and must be compensated for by an increase in their metab- 

 olism. This in turn necessitates a greater consumption of O and production of 

 CO2. Thus, while an animal weighing 2.1 kg. gives off 1.02 g. of CO2 for each 

 kilogram of weight in an hour, one weighing 3.1 kg. yields only 1.96 g. in all. 



The respiratory quotient is higher in herbivora (0.9 to 1.0) than in carnivora 

 (0.7 to 0.8) or omnivora (0.8 to 0.9). These differences find their cause in the 

 character of the food, because the formation of CO2 from carbohydrates, upon 

 which herbivora feed, requires the use of all the O for the reduction of the molecules, 

 while the H has already acquired an amount of sufficient to satisfy it. During 

 the disintegration of the fats and proteids, on the other hand, a portion of the O 

 is employed for the oxidation of the H to form H2O. For this reason, the quotient 

 is lowered by a diet rich in proteid material, and heightened by vegetable foods. 

 It must approximate unity (1.0) as soon as a sufficient amount of carbohydrates 

 has been ingested. *For example, since 6 molecules of O oxidize 1 molecule of 



grape sugar (C6H12O6 = 6CO2 + 6H2O), the quotient must be ^^ ^ = 1. In 



the case of the fats which require a much greater number of molecules of O, the 

 quotient must, of course, become smaller. Olein, for example, needs 80 molecules 

 of O to reduce its molecules, as follows: 



C3H5(Ci8H3302)3 = 57CO2 + 52H2O; hence, the quotient must be -^§^ = 

 • 0UU2 



0.712. 



Inasmuch as the proteins vary considerably in their composition and are not 

 oxidized in their entirety in the body, their quotient can only be arrived at by 

 calculation. Thus, it has been estimated that this value in the case of albumin 

 varies between 0.75 and 0.81, in accordance with the degree of disintegration of 

 the substance. During periods of starvation the quotient remains below normal, 

 because all the available carbohydrates have been utilized and the body subsists on 

 its own proteids and fats. The production of CO2 then falls off at a greater rate 

 than the consumption of O. In diabetic patients, whose consumption of carbo- 

 hydrates is at a minimum, the respiratory quotient is very low, namely, 0.6 to 0.7. 

 Hence, it will be seen that the respiratory quotient at any given moment is depend- 

 ent upon the nature of the substances undergoing oxidation. Atwater has fur- 

 nished the following table: 



Starch 1.0 



Cane sugar 1.0 



Glucose 1.0 



Animal fat . 711 



Protein . 809 



In hibernating animals the quotient becomes very small (0.25), because the 

 output of CO2 and the consumption of O are enormously reduced, but the former 

 in a greater measure than the latter. The CO2 output is also diminished during 

 slee-p and more so than the intake of O. The quotient, therefore, becomes smaller 

 than normal. Brief muscular exercise, on the other hand, increases it immediately, 

 because a considerable quantity of carbon dioxid is then washed out of the active 

 tissues. During longer periods of muscular activity the quotient remains prac- 

 tically the same, in spite of the fact that greater amounts of CO2 and O are worked 



