908 METABOLISM. 



experiments, as well as the proofs of the formation of fat from proteins, 

 are also given in Chapter IX. 



According to PFLUGER'S doctrine, the protein can influence the formation of 

 fat only in an indirect way, namely, in that it is consumed instead of the non- 

 nitrogenous bodies and hence the fat and fat-forming carbohydrates are 

 spared. If sufficient protein is introduced with the food to satisfy the total nu- 

 tritive requirements, then the decomposition of fat stops; and if non-nitrogenous 

 food is taken at the same time, this is not consumed, but is stored up in the animal 

 body, the fats as such, and the carbohydrates at least in great part as fat. 

 ir PFLUGER defines the " nutritive requirement " as the smallest quantity of 

 lean meat which produces nitrogenous equilibrium without causing any decom- 

 position of fat or carbohydrates. At rest and at an average temperature it is 

 found in dogs to be 2.073 to 2.099 grams of nitrogen l (in meat fed) per kilo of 

 flesh weight (not body weight, as the fat, which often forms a considerable fraction 

 of the weight of the body, cannot as it were be used as dead measure). Even 

 when the supply of protein is in excess of the nutritive requirements, PFLUGER 

 found that the protein metabolism increases with an increased supply until 

 the limit of digestive power is reached, which limit is about 2600 grams of meat 

 with a dog weighing 30 kilos. In these experiments of PFLUGER'S not all of the 

 excess of protein introduced was completely decomposed, but a part was retained 

 by the body. PFLUGER therefore defends the proposition " that a supply of 

 proteins only, without fat or carbohydrate does not exclude a protein fattening." 



From what has been said on protein metabolism in starvation and 

 with exclusive protein food, it follows that the protein catabolism in the 

 animal body never stops, that the extent is dependent in the first place 

 upon the extent of protein supply, and that the animal body has the prop- 

 erty, within wide limits, of accommodating the protein catabolism to the 

 protein supply. 



These and certain other peculiarities of protein catabolism have led 

 VOIT to the view that not all proteins in the body are decomposed with 

 the same ease. VOIT differentiates between the proteins fixed in the 

 tissue-elements, so-called organized proteins, tissue-proteins, from those 

 proteins which circulate with the fluids in the body and its tissues and 

 which are taken up by the living cells of the tissues, from the interstitial 

 fluids washing them, and destroyed. These circulating proteins or supply 

 proteins are, he claims, more easily and quickly destroyed than the tissue- 

 proteins. When, therefore, in a fasting animal which has been previously 

 fed with meat, an abundant and quickly decreasing decomposition of 

 proteins takes place, while in the further course of starvation this protein 

 catabolism becomes less in quantity and more uniform, this depends upon 

 the fact that the supply of circulating proteins is destroyed chiefly in the 

 first days of starvation and the tissue-proteins in the last days. 



The tissue-elements constitute an apparatus of a relatively stable 

 nature, which has the power of taking proteins from the fluids washing 

 the tissues and appropriating them, while their own proteins, the tissue- 



1 See Schondorflt, Pfluger's Arch., 71. 



