ELEMENTARY VITAL PHENOMENA 163 



conjecture with great probability as to the synthesis of hippuric 

 acid, which arises from the decomposition of proteids, especially in 

 the metabolism of herbivora. By boiling with mineral acids or 

 alkalies hippuric acid is split into benzoic acid and glycocoll by 

 hydrolysis, and by heating under a high pressure these two sub- 

 stances can again be united into hippuric acid with the loss of 

 water. It is, therefore, supposed that in the body of the herbi- 

 vore, where the possibility exists of the derivation of benzoic acid 

 from proteid or the aromatic compounds of the food, and of glycocoll 

 from gelatine-yielding substances derived from proteid, hippuric 

 acid is formed synthetically from these two substances. As a 

 matter of fact, not only in the body of the herbivore, but even in the 

 carnivore, the formation of hippuric acid may be brought about 

 artificially by introducing benzoic acid into the stomach, this acid 

 then uniting with glycocoll into hippuric acid in an unknown 

 manner in the tissues. In contrast with this, nothing whatever is 

 known concerning the origin of creatin. Creatin, together with 

 creatinin, which is derived from it with loss of water, is the sub- 

 stance in which muscle-cells give off chiefly the nitrogen that comes 

 from the decomposition of their proteid. Just as little is known 

 concerning its fate as concerning its origin ; for, although it is 

 found in muscles in considerable quantity, only small quantities of 

 it appear in the urine ; hence it appears to undergo in some manner 

 transformations in the body itself. Finally, regarding the nuclein 

 bases, it is known only that they are derived from the decompo- 

 sition of nucleins and their derivatives ; the details of the process 

 are unknown. 



Among the non-nitrogenous transformation-products of proteids, 

 the most important are fats, carbohydrates, lactic acid, and carbonic 

 acid. These also are derived from the proteid molecule, not by a 

 simple cleavage but by rearrangement and synthetic processes. The 

 theory th&kfat can arise from proteid by transformation has been 

 much disputed. The pathological process of the so-called fat- 

 metamorphosis of cells, in which fat appears in the place of proteid, 

 so that at the end of the process the cells are dead and filled with 

 fat, necessarily led to the idea that here proteid is transformed into 

 fat. But the objection was possible that in the course of the 

 disease the proteid of the cell is forced out by the fat coming in 

 from the outside. Notwithstanding this possibility, this important 

 question has been decided experimentally in favour of the former 

 view. Leo ('85) made experimental use of the fact that phos- 

 phorus poisoning causes an extremely rapid fat-metamorphosis, 

 especially of the liver-cells. From a number of frogs he selected 

 six individuals of equal size and weight, killed them and deter- 

 mined their fat-contents. He then took six other individuals, 

 poisoned them with phosphorus and killed them after three days. 

 The determination of fat revealed a considerably greater fat- 



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