CIIAP. L] DIGESTION. 241 



does take place in the stomach, the great mass of the fat of a meal 

 is not so changed. 



Such minerals as are soluble in free hydrochloric acid are for 

 the most part dissolved ; though there is a difference in this and in 

 some other respects between gastric juice and simple free hydro- 

 chloric acid diluted with water to the same degree of acidity as the 

 juice, the presence either of the pepsin or other bodies apparently 

 modifying the solvent action of the acid. 



The essential property of gastric juice is the power of dissolving 

 proteid matters, and of converting them into a substance called 

 peptone. 



Action of gastric juice on proteids. The results are essen- 

 tially the same whether natural juice obtained by means of a 

 fistula or artificial juice, i.e. an acid infusion of the mucous mem- 

 brane of the stomach, be used. 



Artificial gastric juice "may be prepared in any of the following 

 ways. 



1. The mucous membrane of a pig's or dog's stomach is removed 

 from the muscular coat, finely minced, rubbed in a mortar with 

 pounded glass and extracted with water. The aqueous extract filtered 

 and acidulated (it is in itself somewhat acid), until it has a free acidity 

 corresponding to '2 p. c. of hydrochloric acid, contains but little of the 

 products of digestion such as peptone, but is fairly potent. 



2. The mucous membrane similarly prepared and minced, allowed 

 to digest at 35 C. in a large quantity of hydrochloric acid diluted 

 to "2 p. c. The greater part of the membrane disappears, shreds only 

 being left, and the somewhat opalescent liquid can be decanted and 

 filtered. The filtrate has powerful digestive (peptic) properties, but 

 contains a considerable amount of the products of digestion (peptone, 

 tfcc.), arising from the digestion of the mucous membrane itself 1 . 



3. From the mucous membrane, similarly prepared and minced, 

 the superfluous moisture is removed with blotting paper, and the pieces 

 are thrown into a comparatively large quantity of concentrated 

 glycerine, and allowed to stand. The membrane may be previously 

 dehydrated by being allowed to stand under alcohol, but this is not 

 necessary. The decanted clear glycerine, in which a comparatively 

 small quantity of the ordinary proteids of the mucous membrane are 

 dissolved, if added to hydrochloric acid of "2 p. c. (about 1 c.c. of 

 glycerine to 100 c.c. of the dilute acid are sufficient), makes an artificial 

 juice tolerably free from ordinary proteids and peptone, and of remark- 

 able potency, the presence of the glycerine not interfering with the 

 results. 



If a few shreds of fibrin, obtained by whipping blood, after 

 being thoroughly washed and boiled, be thrown into a quantity of 

 gastric juice, and the mixture be exposed to a temperature of from 



1 These however may be removed by concentration at 40 C., and subsequent 

 dialysis. 



F. 16 



