ELEMENTARY VITAL PHENOMENA 175 



Gaglio ('86), already mentioned. But the sarco-lactic acid is 

 still further transformed in the body, for, as has been seen, the 

 experiments of Minkowski ('86) upon geese in which the liver 

 was extirpated have shown that lactic acid, presumably combined 

 mth ammonia, is consumed in the synthesis of uric acid. 



The nitrogenous products of proteid-decomposition are the well- 

 known substances which have already been met with frequently, 

 especially urea, uric acid, hippuric acid, creatin, and the nuclein 

 bases, xanthin, hypoxanthin or sarkin, adenin, and guanin. These 

 are excreted chiefly in the urine and represent the compounds in 

 which all the nitrogen taken in in the food leaves the bod}-, 

 apart from an inconsiderable quantity in the sweat and the faeces. 



The last fact, that, with the exception of the minute quantity 

 in the sweat and the faeces, all the nitrogen is excreted in the 

 urine, has assumed great importance in the physiology of animal 

 organisms in connection with the circumstance that proteids 

 and their derivatives are the sole nitrogenous substances in 

 organisms. But, unfortunately, it has led to a false conclusion, 

 which in itself would, perhaps, have had no immediate influence 

 upon the development of fundamental physiological ideas, had not 

 far-reaching and weighty deductions been drawn from it. It 

 follows necessarily from the above-mentioned fact that all 

 nitrogen excreted in the urine must be derived from the decom- 

 position of proteid ; but the further conclusion which, it has been 

 thought, must be drawn from it, does not follow, namely, that the 

 nitrogen excreted in the urine is a measure of the jDi'oteid-trans- 

 formation in the body. The latter conclusion would be justified 

 only if it were known that all nitrogenous cleavage-products of 

 the proteid molecule, without exception, leave the body. But 

 there is no ground for such a belief; on the contrary, no fact what- 

 ever is known which contradicts the idea that nitrogenous cleavage- 

 products of the proteid molecule can rebuild themselves syw- 

 thetically again into proteid with the aid of new non-nitrogenous 

 groups of atoms. This latter possibility has been overlooked, and 

 in consequence ^'iews have arisen, especially in relation to meta- 

 bolism in muscle, which, a priori, bear in themselves the stamp 

 of improbability, but which have been accepted and handed 

 down. Recently they have been attacked and criticised by 

 Pfluger ('91). 



To the excretory substances resulting from retrogressive pro- 

 teid metamorphosis one more group can be added, the members 

 of which likewise are derived from the transformation of proteids, 

 chiefly in the metabolism of bacteria. These are the so-called 

 ptomaines, some of which, on account of their very poisonous action, 

 have lately been termed toxines. Upon their poisonous action 

 chiefly depends the serious illness in the infectious diseases pro- 

 duced by bacteria, such as cholera, dysentery, diphtheria, and 



ft. 



