PEPSIN. 1031 



Wasmann, who first succeeded in isolating it ; his observations 

 were made upon the mucous membrane of the stomach of the 

 pig, which greatly resembles that of man.* The organ which 

 secretes the gastric juice consists of glands of a particular 

 nature contained in the mucous membrane of a portion of 

 the stomach. When this membrane is digested in a large 

 quantity of water at from 86 to 95, without being cut into 

 pieces, but after being well washed, water extracts from it a 

 variety of matters besides pepsin ; but if this water be removed 

 and fresh water added and the digestion continued in the cold, 

 nothing almost dissolves now except pepsin. The operation 

 may be continued with new portions of water till the membrane 

 enters into putrefaction ; water extracts pepsin at every repe- 

 tition till at last nothing remains but a tissue, from which 

 hydrochloric acid takes up no matter capable of dissolving hard- 

 boiled albumen. 



The solution of pepsin, thus obtained from the glandular 

 membrane, is colourless, somewhat viscid, and is capable, if ren- 

 dered acid by hydrochloric acid, of dissolving solid albumen very 

 rapidly. It contains besides pepsin a little albumen, which can 

 be separated from the acid solution by ferrocyanide of potassium, 

 a salt which does not precipitate pepsin, or by heating the 

 solution, if not very dilute, to 1/0, or to 212 without boiling ; 

 the coagulated albumen is then deposited in flocks, with a 

 little modified casein. The filtered liquid is no longer viscid, 

 but preserves the property of dissolving soli4 albumeft with 

 the aid of a little hydrochloric acid. When boiled it becomes 

 turbid again, and loses entirely the power to dissolve the 

 albumen. For when the coagulated flocks are dissolved in 

 acetic acid, they exert no solvent action on hard white of egg, 

 even with the concurrence of hydrochloric acid ; the solution 

 of coagulated pepsin in acetic acid is not precipitated by ferro- 

 cyanide of potassium. 



Pepsin thus appears to be a substance sparingly soluble in 

 water. When its solution is evaporated to dryness, there 

 remains a brown, greyish, viscid mass with the odour of glue 

 and having the appearance of an extract. The solution of the 

 latter in water is turbid, and still possesses a portion of the 

 characteristic power of pepsin, but greatly reduced. On adding 

 * Pharroae. centr. BJatt. 1831). p. 349, 353. 



