366 DIGESTION OF PROTEIDS, [BOOK 11. 



artificial juice, i.e. an acid infusion of the mucous membrane 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 is 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, &c.), arising 

 from the digestion of the mucous membrane itself 1 . 



3. The mucous membrane, similarly prepared and minced, is 

 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, and a 

 too prolonged action of the alcohol injures or even destroys the activity 

 of the product. 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 the 

 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. 



Before proceeding to study the action -of gastric juice on pro- 

 teids it will be useful to review very briefly the chief characters of 

 the more important members of the group. 



The more important proteids which we have thus far studied 

 are: 1. Fibrin, insoluble in water and not really soluble (i.e. 

 without change) in saMne solutions. 2. Myosin, insoluble in 

 water but soluble in saline solutions, provided these are not too 

 dilute or too concentrated. 3. Globulin (including para-globulin, 

 fibrinogen &c.), insoluble in water, but readily soluble in even very 

 dilute saline solutions. 4. Albumin, serum-albumin, soluble in 

 water in the absence of all salts. 5. Acid-albumin, into which 

 globulins and myosin are rapidly converted by the action of dilute 

 acids, the particular acid-albumin into which the myosin of muscle 

 is changed being sometimes called syntonin. If the reagent used 

 be not dilute acid but dilute alkali, the product is called alkali- 

 albumin. The two bodies, acid-albumin and alkali-albumin, are 

 very parallel in their characters, and may readily be converted 



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

 dialysis. 



