128 THE DIGESTIVE FLUIDS. 



v. WITTICH'S METHOD. The mucous membrane of a pig's 

 stomach is carefully dissected off, freed from mucus by washing 

 with water, hashed, robbed together with pure quartz sand, and 

 finally treated with glycerin, containing 0.1 per cent, of hydrochloric 

 acid, in the proportion of 10-20 grammes for 1 part of mucous 

 membrane. The mixture is kept at a temperature of 40 C. for 

 from one to two weeks, when it is filtered. The extract which is 

 thus obtained may then be used for experimental purposes by 

 diluting with 0.10.4 per cent, of hydrochloric acid, in the propor- 

 tion of 2-3 : 100. 



To obtain as pure a preparation as possible, Briicke's method, 

 or one of its many modifications, is usually employed. But it is 

 to be noted, as Gautier has pointed out, that while the substance 

 is thus obtained in large amount, it is but little active. We find, 

 as a matter of fact, that a small flake of fibrin, which has been 

 previously caused to swell by placing it in dilute hydrochloric acid, 

 dissolves in a solution of Briicke's pepsin only after five minutes, 

 while other and more impure preparations are decidedly more 

 effective. Briicke's method is as follows : 



BRUCKE'S METHOD. The mucous membrane, which has been 

 carefully dissected off and washed with water, is placed in a solu- 

 tion of dilute phosphoric acid (12 pro mille) and allowed to stand 

 for about one week. By this time digestion has usually proceeded 

 to a point where a precipitate is no longer obtained on render- 

 ing the mixture nearly neutral with sodium hydrate. It is then 

 neutralized with lime-water, which causes a precipitation of cal- 

 cium phosphate, while the pepsin is at the same time carried 

 down mechanically, and adheres so firmly to the phosphates that 

 these can subsequently be washed with water without losing any 

 of the pepsin. The precipitate is then dissolved in dilute hydro- 

 chloric acid, and the solution dialyzed until the phosphates and 

 the hydrochloric acid have diffused out. The remaining solution, 

 which contains the pepsin, is now treated with large quantities of 

 strong alcohol. In this manner the ferment is precipitated, and 

 is readily collected on a filter. 



Other ferments, such as ptyalin, do not adhere to the phosphates 

 so firmly as pepsin, and can hence be removed by suspending the 

 precipitate in water and passing a current of air through the solu- 

 tion for some time. 



Instead of dialyzing the acid solution, as just described, and 

 then precipitating with alcohol, it is also possible to obtain the 

 ferment by treating such acid solutions with a concentrated alco- 

 holic-ethereal solution of cholesterin. When this is added the 

 cholesterin is immediately thrown down, and carries the pepsin 

 with it. If this precipitate is then collected on a filter and 

 washed with alcohol, the cholesterin is dissolved, while the ferment 

 remains. 



Such preparations, however, are impure, and probably contain 



