322 DIGESTION OF PROTEIDS. [BOOK n. 



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 Ir^drochloric 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 h3 T drochloric acid of -2 p.c. (about 

 1 c.c. of the glycerine to 100 c.c. of the dilute acid is sufficient), makes 

 an artificial juice tolerably free from ordinary proteids and peptone, 

 and of remarkable potency, the presence of the glycerine not interfer- 

 ing 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 saline solutions. 2. Myosin, insoluble in 

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

 dilute or too concentrated. 3. Globulin (including paraglobulin, 

 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 

 the one into the other by the use of dilute alkali or dilute acid 

 respectively. Their most important common characters are in- 

 solubility in water and in saline solutions and ready solubility in 

 dilute acids and alkalis. 6. Coagulated proteids. As we have 

 seen, when fibrin suspended in water, serum-albumin in solution, 



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

 dialysis. 



