48 PROTEIDS. 



Purified lardacein is readily soluble in moderately dilute ammonia, 

 and can, by evaporation, be obtained from this solution in the form of 

 tough, gelatinous flakes and lumps ; in this form it gives feeble re- 

 actions only with iodine. If the excess of ammonia is expelled, the 

 solution becomes neutral, and is precipitated by dilute acids. 



Preparation. The gland or other tissue containing this body is 

 cut up into small pieces, and as much as possible of the surrounding- 

 tissue removed. The pieces are then extracted several times with 

 water and dilute alcohol, and if not thus rendered colourless, are 

 repeatedly boiled with alcohol containing hydrochloric acid. The 

 residue after this operation is digested at 40 C., with active artificial 

 gastric juice in excess. Everything except lardacein, and small 

 quantities of mucin, nuclein, keratin, together with some portion of i 

 the elastic tissue, will thus be dissolved and removed 1 . From the 

 latter impurities it may be separated by fractional decantation of the 

 finely-powdered substance from water, alcohol and ether. 



In opposition to the older statements it has recently been stated 

 that lardacein may be digested by pepsin in presence of hydrochloric 

 acid 2 . The writer's own experiments lead him to believe in the results 

 obtained by the earlier authorities. 



The known products of decomposition of proteids are very nume- 

 rous, varying in nature and relative amount with the conditions 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. 

 These products belong for the most part to well-known classes of 

 chemical substances and in many cases representatives of several 

 consecutive members of any given homologous series are obtained 

 during the decompositions. 



A study of these products has not however up to the present time 

 thrown any extended light upon the more minute molecular structure 

 of the proteids, and the reason is not far to seek. It consists simply 

 in the fact that we possess no guarantee or criterion of the purity of 

 those proteids which can be obtained in sufficient amounts for the 

 purposes of experiment. They may be, and probably are, mixtures of 

 it may be several closely allied substances, so that the numerous 

 products which arise during the decomposition of what is regarded in 

 the experiment as one uniform substance, represent really the decom- 



1 Kiihne and Kudneff, Virchow's Arch. Bd. xxxm. (1865), S. 66. 



2 Kostjurin, Wien. med. Jahrb. 1886, S. 181. 



