CHAP. II.] METHODS OF PREPARING PEPSIN. 85 



SECT. 7. AN ACCOUNT OF v THE ATTEMPTS TO SEPARATE PEPSIN, 



AND TO ESTABLISH ITS CHARACTERS. 



Pepsin. 



Eberle was the first, as we have seen, to shew that the mucous 

 membrane of the stomach undergoes solution under the influence 

 of dilute acids, and he described a mode of obtaining an artificial 

 gastric juice which possessed the power of digesting suitable sub- 

 stances at a proper temperature. His experiments were, however, 

 concerned rather with the behaviour towards chemical reagents of 

 his artificial gastric juice than with the study of its real digestive 

 activity, the nature of which he much misunderstood. Schwann, we 

 have also seen, almost immediately afterwards took up the investi- 

 gation of artificial gastric juice. ' He pointed out that the mucous 

 membrane of the stomach alone was capable of yielding an artificial 

 gastric juice ; that it did not, as Eberle had thought, share this pro- 

 perty with other mucous membranes, and he set about trying to 

 isolate the principle which conferred upon dilute acids the property 

 of dissolving certain of the food constituents. 



schwann's The mucous membrane of the stomach was digested 



attempts to in water, and the aqueous solution was treated with 

 isolate the ferrocyanide of potassium, so as to precipitate the 

 .gestive fer- p rote i<j s present in the solution. The fluid was filtered, 

 and the filtrate was neutralized with potassium car- 

 bonate; it was then precipitated with a solution of corrosive sub- 

 limate. The precipitate produced by this body was suspended in 

 dilute hydrochloric acid and decomposed by means of sulphuretted 

 hydrogen. The solution filtered from sulphide of mercury possessed 

 intense proteolytic activity. To the proximate principle present in 

 the mucous membrane of the stomach, which he in some degree 

 had separated by his process, Schwann gave the name of Pepsin, 

 without however laying any pretence to having isolated it. 



Wasmann's By a modification of Schwann's method, Wasmann 1 



method of pre- soon after succeeded in obtaining a soluble solid pepsin, 

 paring pepsin, possessed of very intense activity. 



The mucous membrane from the fundus of a pig's stomach, was 

 carefully dissected off and treated with water at 30 40 C., and 

 after some hours the liquid was poured off, the mucous membrane 

 being thereafter treated again and again with cold water. The 

 united watery liquids were precipitated with lead acetate or mercuric 



1 Wasmann, De digestione nonnulla, Diss. Inaug., Berolini, 1839. The author has 

 not been able to see this dissertation. The account of Wasmann's pepsin given in the 

 text is taken almost verbatim from Maly, 'Chemie der Verdauung,' Hermann's 

 Handbuch, Vol. v. Part ii. (1881), p. 44. 



