32 HANDBOOK FOR BIO-CHEMICAL LABORATORY. 



suspended in water, and treated with HOI until it just dis- 

 solves. The solution is then poured into a saturated solution 

 of cholesterin, made by dissolving it in a mixture of 4 parts 

 alcohol and 1 part ether. A precipitate of cholesterin will be 

 formed on the addition of the above acid solution, and this is 

 repeatedly shaken with the liquid, and the cholesterin will 

 mechanically carry down with it a part at least of the pepsin 

 in solution. Collect this on a filter, wash with water, then 

 with acetic acid, and lastly with water again until the wash- 

 water gives no further reaction for HOI with AgN0 3 . 



The moist cholesterin precipitate is shaken in a separatory 

 funnel with ether. Two layers will form the upper an 

 ethereal solution of cholesterin and the lower an aqueous 

 solution of pepsin. Separate the two and shake the aqueous 

 solution repeatedly with ether until all traces of cholesterin 

 are removed. The turbid aqueous solution is now filtered, 

 and when acidulated possesses proteolytic activity. When 

 allowed to evaporate spontaneously it leaves a grayish, amor- 

 phous, non -hygroscopic nitrogenous body. (Brucke.) 



2. The finely divided mucous membrane of the fundus of 

 the stomach is extracted with glycerin, or, better, with 

 glycerin containing 1 p.m. HC1. Add 10 to 20 parts glycerin 

 for every part by weight of the mucous coat and allow to 

 stand for 8 to 14 days. Filter and precipitate the pepsin from 

 the glycerin extract by the addition of a large excess of abso- 

 lute alcohol. This may be purified by dialysis through parch- 

 ment paper, (v. Wittich.) 



Artificial Gastric Juice. 



Preparation. 1. The mucous membrane from the cardiac 

 region of five or six pigs' stomachs is finely divided and then 

 digested for two weeks, at 40 C., with two to three litres of 

 0. 5$ hydrochloric acid. At the end of this time all but traces 

 of albumoses have been converted into peptones, which are in 



