12 



MAINTENANCE RATIONS OF FARM ANIMALS. 



Protein katabolism of dog m per cent of total katabolism. 



Number of cases. 



Absolute. 



Per cent. 



Less than 10 per cent . 



10 to 14 per cent 



14 to 17 per cent 



More tban 17 per cent 



4 

 15 



5 

 3 



14.8 

 55.6 

 18.5 

 11.1 



27 



100.0 



It may be accepted as established, then, that in what may be spoken 

 of as the normal fasting animal, in which the influence of the pre- 

 vious feeding has disappeared and in which, on the other hand, the 

 fat reserve has not been exhausted, the protein katabolism constitutes 

 a fairly small percentage of the total katabolism, both being ex- 

 pressed in terms of energy. 



It is clear, however, from the foregoing figures that the ratio of 

 protein to total katabolism may vary considerably. The most impor- 

 tant factor in this variation has been found to be the relative amount 

 of fat contained in the body. So long as fuel material in the form 

 of body fat is readily available, the amount of protein katabolized 

 remains small. Usually, however, the store of fat in the body is less 

 than that of protein, while in fasting its exhaustion is relatively 

 more rapid. There comes a time, therefore, when the supply of non- 

 nitrogenous material to the tissues begins to flag. When this hap- 

 pens, the protein katabolism begins to increase — that is, when the 

 supply of reserve fuel material runs low the organism begins to use 

 the protein of its own tissues as a source of energy, and E. Voit 1 

 shows that this occurs whenever the ratio of fat to protein remain- 

 ing in the body falls below a certain limit. If the animal was origi- 

 nally well fed, this rise in the protein katabolism occurs only shortly 

 before death, from which fact it has received the name of the pre- 

 mortal rise. In the case of very fat animals this point may never 

 be reached, while, on the other hand, in a lean animal the protein 

 katabolism may increase steadily from the very beginning of the 

 fasting. The following three experiments upon a fat guinea pig, a 

 moderately fat dog, and a lean rabbit, cited by Voit from Kubner's 

 experiments, may serve to illustrate these three types of fasting 

 katabolism : 



INFLUENCE OF BODY FAT. 



1 Loc. Cit, p. 502. 



