86 METHODS OF PREPARING PEPSIN. [BOOK II. 



chloride, the precipitate containing lead or mercury compounds of 

 proteids, entangling peptones, was collected, suspended in water, and 

 decomposed by means of sulphuretted hydrogen, and from the filtrate 

 after concentration, pepsin (mixed with proteids) was precipitated by 

 means of alcohol. 



The precipitated flocculi when dried yielded a yellow, gum-like 

 matter. Acids caused a turbidity in the solution of this pepsin, 

 metallic salts produced a precipitate. 



According to Wasmann the proteolytic action of his pepsin was 

 so great that one part in 60,000 of water, when acidulated, dissolved 

 coagulated albumin in from six to eight hours. 



By Wasmann's method, as by all other methods yet suggested, 

 it is impossible to prepare pure pepsin though unquestionably, 

 assuming his assertions to be correct, his method yielded him an 

 extraordinarily potent product. 



Briicke's 1 The mucous membrane of the pig's stomach is 



method of iso- separated from the subjacent muscular coat, and after 

 lating pepsin. ca reful washing and removal of the adhering water by 

 pressing between blotting-paper, is finely divided, preferably in a 

 mincing machine. The mass is then digested in a 5 per cent, solution 

 of tribasic phosphoric acid, at a temperature of 35 C., until nearly 

 the whole is dissolved. The solution contains all the pepsin in 

 solution, together with large quantities of parapeptones and pep- 

 tones. The acid fluid is almost neutralized by the addition of lime- 

 water, which causes a precipitate of Ca 3 (P0 4 ) 2 . This precipitate 

 carries down with it much of the pepsin previously dissolved, whilst 

 a considerable portion of the parapeptones and the whole of the 

 peptones are left in the solution. The gelatinous precipitate is 

 carefully washed with water, pressed, suspended in water and HC1 

 added until it just dissolves. The solution is then poured little by 

 little to the bottom of a tube containing a saturated solution of 

 cholesterin made by dissolving that body in a mixture of four parts 

 of alcohol and one part of ether. When the slightly acid aqueous 

 solution comes in contact with the ethero-alcoholic liquid it produces 

 a precipitate of cholesterin ; this precipitate is repeatedly shaken 

 up with the liquid in which it is produced. The cholesterin which 

 has carried down with it mechanically a part at least of the pepsin 

 originally present, is collected on a filter and is washed first with 

 water, then with acetic acid, and lastly again with water, until the 

 wash-waters are no longer acid and give no turbidity when treated 

 with silver nitrate. 



The moist cholesterin is now shaken up in a stoppered bottle 

 with pure ether. The liquid in the bottle then separates into two 

 layers, the upper of which is composed of an ethereal solution of 

 cholesterin, the lower of water (which had adhered to the cholesterin) 

 holding pepsin in solution. The ethereal layer is separated from the 



1 Briicke, Vorlesungen, Vol. n. p. 300. 



