1030 PEPSIN, GLOBULIN, &C. 



finds that the pellicle is formed by the absorption of oxygen, 

 and does not appear upon milk heated in an atmosphere of car- 

 bonic acid. 



Fresh and pure blood-serum, mixed with twice its weight of 

 distilled water, and a small quantity of a solution of caustic 

 alkali, soon loses all alkaline reaction, and on heating to the 

 boiling point, the coagulation of the albumen no longer occurs ; 

 but the solution when heated becomes covered by a pellicle, 

 like milk. M. Scherer considers this as the conversion of albu- 

 men into casein, the pellicle agreeing closely in composition and 

 properties with the pellicle from heated milk. 



M. Scherer also finds soluble casein, always to leave, when 

 burnt, a highly alkaline ash containing much lime, but in the 

 coagulated state to leave a neutral ash. The solubility of the 

 casein he, therefore, ascribes to its combination with an alkali, 

 and its coagulation to the saturation of that alkali. The acid 

 which saturates the alkali appears to be the lactic, produced by 

 the change of the sugar of milk, under exposure to air, when the 

 milk is heated. 



SECTION III. 



PEPSIN, GLOBULIN, HEMATOSIN, GELATIN, CHONDRIN. 

 PEPSIN. 



This is a peculiar animal principle secreted by the stomach 

 and present in the gastric juice. It is usually prepared by 

 infusing the mucous membrane of the fourth stomach of the 

 calf, which is known as rennet, and as obtained from this source 

 is distinguished by the power which it possesses to coagulate 

 milk. This property the infusion loses when boiled, indicating 

 a relation between pepsin and albumen. The infusion, aided 

 with a few drops of hydrochloric acid, and kept at 80 or 90, dis- 

 solves completely portions of albumen boiled hard, of fibrin or 

 boiled meat, in the course of from 1 2 to 24 hours. By means 

 of this agent the process of animal digestion has been imitated 

 perfectly, out of the body, by Eberle, Schwann and other 

 physiological inquirers. 



The most precise information we possess respecting the 

 nature and production of pepsin has been obtained by M. 



