192 CHEMISTRY OF THE PROTEIDS CHAP. 



of digestion. Both plasteins give the biuret and lead sulphide 

 reaction, as also the tests of Molisch and Adamkiewicz. The per- 

 centage compositions of A and B plasteins is : 



C H N S 



Aplastein . 58'8 7'3 14'4 1-24 

 B plastein . 58'9 7'2 14'3 not determined. 



On adding papayotin to an albumose solution, which was prepared by 

 digesting egg-albumin for three days, a small amount of ' coagulose 

 was obtained, which was partly soluble in dilute soda-solution. 



The precipitate in question, according to Lawrow and Salaskin, is 

 not a restituted or reformed albumin, but an albumose which can be 

 dissociated by erepsin. Umber found its amount to run parallel to the 

 amount of hetero-albumose contained in any given albumin, and con- 

 sidered it to be a precursor of hetero-albumose. Sawjalow likewise 

 obtained plastein in larger quantities only from the hetero-albumose ; 

 while from the other albumoses, which were by no means pure, only 

 traces could be got. The precipitate is therefore either heteip-albumose 

 or that portion of the acid-albumin which belongs to the anti-group, 

 and which during metabolism is converted into hetero-albumose. 



The coagulation of albumose by means of extracts of various 

 organs, which had undergone auto-digestion for sixteen hours, has 

 been studied by Niirnberg. 1 The extracts acted in the following 

 descending order : Extracts from the liver, stomach, lungs, pancreas, 

 small intestine, large intestine, kidney, brain, eggs, and muscle. Milk 

 is most acted upon by pancreas extracts, less by fresh gastric extract, 

 and hardly at all by other extracts. 



While all the observers mentioned so far have found what they 

 term plastein to be an albumose-like substance, Bayer 2 has isolated a 

 plasteinogenous compound which is a peptoid (peptid), i.e. one of those 

 dissociation products of albumin which are formed in large amounts 

 during the early stages of peptic digestion (Zunz), and which give no 

 biuret-reaction. 



To obtain this peptoidal plastein Bayer proceeded as follows : 

 (1) a 10 per cent watery solution of Witte's peptone was precipitated 

 with an equal bulk of 95 per cent alcohol ; (2) the alcoholic filtrate 

 mixed with twice its volume of acetone ; (3) the alcohol-acetone 

 filtrate precipitated with 80 per cent alcohol. The final filtrate con- 

 tains the plastein, which gives neither the biuret, nor the xantho- 

 proteic, lead-sulphide, Millon's and Molisch's reactions. 



1 A. Niirnberg, Hofmeister's Beitrage, 4. 543 (1904). 

 2 H. Bayer, ibid. 4. 554 (1904). 



