53$ WASTE-PRODUCTS 



hence the respiratory quotient for the oxidation of pure carbohydrates 

 is equal to unity. This probably represents the maximal value of the 

 respiratory coefficient which may be obtained with normal animal tis- 

 sues. Figures in excess of this which have occasionally been observed 

 have been attributed by some observers to the formation in the tissues 

 of fat from carbohdrates with the liberation of carbon dioxide: 



+ O 2 = Ci6H 32 O 2 + 8CO 2 + 8H 2 O 

 Glucose. Palmitic acid. 



Respiratory quotients in excess of unity have been observed in hiber- 

 nating animals immediately prior to their winter-sleep, and in animals 

 and birds fed with an enormous excess of carbohydrates. 



The respiratory quotient for the oxidation of Fats is necessarily 

 much lower than it is for carbohydrates, since the fats do not contain 

 more than about one-sixth of the oxygen which is required to convert 

 the hydrogen which they contain into water. An important proportion 

 of the absorbed oxygen is therefore excreted in the form of water, and 

 the carbon dioxide which is discharged from the body falls very much 

 short of the molecular equivalent of the oxygen absorbed, the respira- 

 tory quotient for the ordinary dietary fats being 0.71. The Proteins 

 contain about half the oxygen needed to oxidize their hydrogen and the 

 respiratory quotient is intermediate between the value for carbohydrate 

 and fats, namely 0.81. 'The respiratory quotient for Alcohol is lower 

 even than for fats, namely 0.67. 



From these considerations it is evident that the value of the respira- 

 tory coefficient must be capable of yielding important information as 

 to the particular class of foodstuffs which is being utilized for the 

 performance of a given function. Thus for man, under ordinary con- 

 ditions of work and nourishment, the respiratory quotient lies between 

 0.8 and 0.9, but when hard Muscular Work is being performed it rises 

 and may even approach the ideal value of unity for the oxidation of 

 carbohydrates. Part of this rise, especially during the initial stages 

 of a work-experiment, or in experiments occupying only a short period, 

 may possibly be ascribed to the "washing out" of carbon dioxide 

 accumulations from the tissues by the more rapid respiratory and 

 cardiac movements. It must be recollected, however, that the rapidity 

 of the respiratory movements in exercise is conditioned by the enhance- 

 ment of the carbon-dioxide content of the blood, so that but a slight 

 proportion of the increased carbon-dioxide output during exercise can 

 justifiably be attributed to the increased ventilation of the body, and, 

 furthermore, the effect of muscular work upon the respiratory quotient 

 endures for a long period, until in fact, the carbohydrate-reserves have 

 been so far depleted that we may surmise that other foodstuffs are 

 now being utilized for the production of muscular energy. The rise 

 of the respiratory quotient during the performance of muscular work 

 therefore affords us confirmatory evidence of the view that muscular 



