DIGESTION. 179 



active and not liable to spoil may be obtained if, as suggested by 

 v. WITTICHS, we extract the finely-divided mucous membrane with 

 glycerin, or better with glycerin which contains 1 p. m. HC1. To 

 each part by weight of the mucous coat add 10-20 parts glycerin. 

 This is filtered after 8-14 days. The pepsin (together with mucli 

 albumin) may be precipitated by alcohol from this extract. If this 

 extract is to be used directly for digestion tests, then to 100 c. c. of 

 water which has been acidified with 1-4 p. m. HC1 add 2-3 c. c. of 

 the extract. 



For digestion tests an infusion of the mucous membrane of the 

 stomach may be used directly in many cases. The mucous coat is 

 carefully washed with water (if a pig's stomach is used) and finely 

 cut; if a calfs stomach is employed, only the upper layer of the 

 mucous coat is scraped off with a watch-glass or the back of a knife. 

 The pieces of mucous membrane or the slimy masses obtained by 

 scraping are rubbed with pure quartz-sand, treated with acidified 

 water, and allowed to stand for 24 hours in a cool place and then 

 filtered. 



In the preparation of artificial gastric juice that part only of the 

 mucous coat richest in pepsin is used, the pyloric is of little value. 

 A strong, impure infusion may generally be obtained from the 

 pig's stomach, while a relatively pure and powerful infusion is ob- 

 tained from the stomach of birds (hens). The stomachs of fish 

 (pike) also yield a tolerably pure and active infusion. An active 

 and rather pure artificial gastric juice may be prepared by scraping 

 the inner layers of a calfs stomach from which the pyloric end has 

 been removed. For a medium-sized calfs stomach 1000 c. c. of 

 acidified water must be used. 



The degree of acidity required in the infusion depends upon 

 the use to which the gastric juice is to be put. If it is to be em- 

 ployed in the digestion of fibrin, an acidity of 1 p. m. HC1 must 

 be selected, while, on the contrary, if it is to be used for the diges- 

 tion of hard -boiled -egg albumin, an acidity of 2-3 p. m. HC1 is 

 preferable. This last-mentioned degree of acidity is generally the 

 better, because the infusion is preserved thereby, and at all events 

 it is so rich in pepsin that it may be diluted with water until it has 

 an acidity of 1 p. m. HC1 without losing any of its solvent action 

 on unboiled fibrin. 



The Action of Pepsin on Proteids. Pepsin is inactive in neutral 

 or alkaline reactions, but in acid liquids it dissolves coagulated 

 albuminous bodies. The proteid always swells and becomes trans- 

 parent before it dissolves. Unboiled fibrin swells up in a solution 

 containing 1 p. m. HC1, forming a gelatinous mass, and does not 

 dissolve at ordinary temperature within a couple of days. Upon 



