RESPIRA TION. 437 



variations not only in different species, but in different individuals under 

 varied circumstances. The chief reasons for the differences are : 



First, the production of C0 2 is in a measure independent of the O absorbed, 

 as is proven by the records of various investigators, showing that C0 2 results 

 both from oxidation-processes and from intramolecular splitting (analogous to 

 fermentation-processes) which may be entirely independent of each other; 

 that the quantity of 0O 2 eliminated may continue under certain circumstances 

 at the normal standard even after the absorption of O has ceased ; and that 

 the quantity of O contained in the C0 2 eliminated during a given time may 

 be larger than the actual quantity absorbed. This may be understood in a 

 general way when we remember that the CC) 2 formed in the body is not the 

 result of an immediate oxidation of the carbon-containing material of the 

 body ; on the contrary, some of the O absorbed may be stored, as it were, in 

 the form of complex compounds, which at some later time may undergo disin- 

 tegration, with the formation of C0 2 ; or the complex materials introduced as 

 food may undergo a similar disintegration and splitting of the molecules, with 

 the formation of C0 2 independently of the direct action of the O upon them. 

 Second, a larger quantity of 0O 2 is formed per unit of oxygen from the 

 disintegration of certain substances than from others, consequently the quotient 

 must be affected by the nature of the substances broken down. Thus, in the 

 formation of C0 2 from carbohydrates all of the O consumed in the disinte- 

 gration of the molecules is used in forming C0 2 , the H already having suffi- 

 cient O to satisfy it ; but in the case of fats and proteids a portion of the O 

 is utilized in the oxidation of H to form H 2 0. 6 molecules of O will oxidize 

 1 molecule of grape-sugar (C 6 H 12 6 ) into 6C0 2 + 6H 2 ; hence the quotient is 



n 2 =1. In regard to fat, if we take olein, C 3 H 5 (C^H^O^, as an ex- 

 ample, 80 molecules of O are required to reduce each molecule of the fat to 



5 7 CO 

 57 molecules of C0 2 and 52 molecules of H 2 ; hence the quotient is - Qnr . 2 



80 (J 2 



= 0.712. In the disintegration of proteid only a part of the C is oxidized 



into C0 2 , the remainder being eliminated as a constituent of various complex 



effete bodies; but it is estimated that the quotient for proteids (albumin) is 



from 0.75 to 0.81, depending upon the completeness of disintegration. 



The respiratory quotient varies with species, food, age, the time of day, 

 internal and external temperature, muscular activity, the composition of the 

 inspired air, etc. 



In regai'd to species, the quotient is higher in warm-blooded (0.70 to LOO) 

 than in cold-blooded animals (0.G5 to 0.75) ; in herbivora (0.90 to 1.00) than 

 in carnivora (0.75 to 0.80) ; and in omnivora (0.80 to 0.90) than in carnivora, 

 but lower than in herbivora. These differences are due essentially to diet, 

 herbivora feeding largely upon carbohydrates, omnivora using carbohydrates 

 to a less extent, and carnivora practically not at all. These observations are 

 substantiated by the fact that during lasting, when the animal is feeding upon 

 its own tissues, the respiratory quotient in all species is the same (0.7 to 0.75). 



