CHEMICAL BASIS OF THE ANIMAL BODY. 1187 



longed putrefaction indole, phenol, etc. On the other hand, it 

 exhibits the following marked differences from other proteids : 

 It wholly resists the action of ordinary digestive fluids ; it is 

 coloured red, not yellow, by iodine, and violet or pure blue 

 by the joint action of iodine and sulphuric acid. From these 

 last reactions it has derived one of its names, 'amyloid,' though 

 this is evidently badly chosen ; for not only does it differ from 

 the starch group in composition, but by no means can it be 

 made to yield sugar : this latter is one of the crucial tests for 

 a true member of the carbohydrate group. 



Purified lardacein is readily soluble in moderately dilute 

 ammonia, and can, by evaporation, be obtained from this solu- 

 tion in the form of tough, gelatinous flakes and lumps ; in this 

 form it gives feeble reactions only with iodine. If the excess 

 of ammonia is expelled, the solution becomes neutral, and is 

 precipitated by dilute acids. 



In opposition to the older statements it has recently been 

 stated that lardacein may be digested by pepsin in presence of 

 hydrochloric acid. 





The known products of decomposition of proteids are very 

 numerous, varying in nature and relative amount with the con- 

 ditions and reagents by means of which they are produced, and 

 it may be similarly, though to a much less extent, with the kind 

 of proteid employed. They belong for the most part to well- 

 known classes of chemical substances and in many cases repre- 

 sentatives of several consecutive members of any given homol- 

 ogous series are obtained during the decompositions. A study 

 of these products has not up to the present time thrown any 

 extended light upon the more minute molecular structure of 

 the proteids and it cannot as yet be said that we possess any 

 real knowledge of their constitution. When proteids are 

 decomposed by mineral acids (HC1, in presence of stannous 

 chloride) at 100, the products formed are chiefly amido-acids 

 such as leucine, tyrosine, glutamic and aspartic acids with 

 some ammonia. (Most recently two new nitrogenous crystalline 

 bases, lysine and lysatine, have been additionally obtained.) 

 The former is probably diamido-caproic acid, the latter a homo- 

 logue of creatine. These bases, as also ammonia, are also 

 formed during a pancreatic digestion of proteids. When de- 

 composed by barium hydroxide in sealed tubes at 200 250, 

 the products already named (except lysine and lysatine) are 

 obtained, together with amido-acids homologous with leucine, 

 leuce'ines (C n H^^NOg), etc., and additionally carbonic, oxalic 

 and acetic acids. 



