178 NUTRITION OF FARM ANIMALS 



fact, while these acids are known to be freely oxidized in the 

 body, the chemical mechanism of the process is little under- 

 stood. 



253. Formation of carbohydrates from fats. In discussing 

 the probability of the formation of carbohydrates from pro- 

 teins (235), it was pointed out that their origin might often be 

 ascribed to either proteins or fats or both. It was there shown 

 that in many cases the probabilities strongly favored a forma- 

 tion from proteins. In other instances, however, the proba- 

 bilities seem equally strong that fats give rise to carbohydrates. 

 In particular, experiments upon pjiloridzin diabetes of the 

 dog have shown the production of more sugar than could be 

 formed from the quantity of protein katabolized during the 

 same time, while the stock of glycogen in the animals experi- 

 mented on had been so exhausted by fasting and muscular work 

 that it seems scarcely possible to interpret the results other- 

 wise than as showing the formation of sugar from fat. It should 

 be added, however, that it has been seriously questioned whether 

 the conditions of the experiments were sufficiently controlled 

 to warrant the conclusions drawn. 



The very low values for the respiratory quotient (296) which 

 have been reported in some cases for hibernating animals have 

 also been interpreted as indicating a production of carbohydrates 

 from fat. In the conversion of fat into sugar, there must ob- 

 viously be an absorption of oxygen with no corresponding evolu- 

 tion of carbon dioxid, the tendency of which would be to lower 

 the respiratory quotient. The value of the latter for the direct 

 oxidation of fat is 0.7. In hibernating animals, however, 

 figures as low as 0.3 have been reported, while the weight of the 

 fasting animal increased. While these facts, of course, do not 

 demonstrate the formation of sugar from fat, they are quite 

 compatible with that interpretation and seem to indicate a 

 storage of oxygen. The more recent experiments on hibernat- 

 ing animals, however, have failed to give such low quotients as 

 were obtained by earlier observers. 



7. METABOLISM OF ASH INGREDIENTS 



254. Certain chemical elements of the body and of the feed 

 are found wholly or in part in their ash when these materials 



