84 



MAINTENANCE RATIONS OF FARM ANIMALS. 



less it is evident that there must be a relatively large loss of body 

 protein in those more moderate cases in which the deprivation of 

 protein is not continued so long as to cause death. Furthermore, 

 the losses occurring in these latter cases may be made good by subse- 

 quent feeding and the animal restored to its original state. Strik- 

 ing examples of the same fact are familiar in the human subject in 

 the emaciation due to long illness and the restoration of the body 

 during convalescence. Pugliese 1 has shown that a similar storage of 

 protein takes place rather rapidly in the liver when a previously 

 fasted animal receives feed again. In brief, it is evident that the 

 body of the mature animal may fluctuate within somewhat wide limits 

 as regards its protein content without necessarily causing any serious 

 or permanent derangement of its functions. 



We can hardly suppose such a fluctuation to consist to any large 

 extent of an actual destruction and rebuilding of the cells of muscu- 

 lar or other tissue, but must regard it as effected chiefly by changes in 

 the amount of cell contents — an alternate atrophy and hypertrophy of 

 the cells under the influence of the changing protein supply. This 

 same conception may be invoked, however, to explain small as well 

 as large fluctuations in the body protein. According to Eubner, 2 

 the cells of the body seek to maintain an optimum protein content, 

 and in proportion as this becomes reduced they show a capacity 

 for storing up protein, when a more abundant supply is offered in 

 the feed, which is analogous to that observed during growth. On the 

 other hand, when the supply of feed protein is insufficient, protein 

 previously stored may be katabolized. 



In other words, as regards its stock of nitrogenous material the 

 organism may exist and function at a higher or lower level accord- 

 ing to the amount of protein supplied in the feed, while for each 

 level of protein stock a certain supply in the feed is necessary — that 

 is, the protein required for maintenance varies. With carnivora on 

 a largely protein diet, such as was used in Voit's experiments, the 

 adjustment of the body to the protein supply seems to take place 

 rather promptly. In the case of herbivora, however, the adjustment 

 appears to be more gradual, possibly owing to the relatively large 

 supply of nonnitrogenous ingredients in their feed, and apparently 

 some gain of protein may continue for a considerable time, although 

 when expressed as a percentage of either the total feed protein or 

 of the body protein the gain is relatively small. 



RELATION TO ENERGY SUPPLY. 



The prime demand of the organism is for energy for the per- 

 formance of its vital functions, and if necessary it will draw upon 

 its own tissues for this purpose. No clear conception of the laws 



1 Jahresbericht fiber die Fortschritte der Tier-Chemie, vol. 34, p. 529. 



2 Das Problem dor Lebensdauer, etc. 



