SEPARA TION OF PEPSIN AND RENNIN. 335 



pepsin ; that is, the pyloric part furnishes very weak extracts compared 

 with those yielded by the fundus. 1 



Solutions of rennin, commonly called rennets, may be prepared by 

 extracting the mucous membrane of the stomach in various ways, of 

 which the following is a summary : 



1. Extraction of the mucous membrane of the stomach of the calf for some 

 days with glycerin. Purer solutions may be afterwards obtained by precipi- 

 tating the glycerin extract with excess of alcohol, filtering, and treating the 

 precipitate with water. 



2. Digesting the mucous membrane of the stomach for twenty-four hours 

 at atmospheric temperature with water containing 1 to 2 parts per mille of 

 hydrochloric acid, filtering, and neutralising. 



3. Extracting with a saturated aqueous solution of salicylic acid, precipi- 

 tating by excess of alcohol, and extracting the precipitate with water. 



4. The best extractive for making permanent preparations is solution of 

 sodium chloride of from 5 to 15 per cent, concentration, putrefaction being 

 prevented by the addition of alcohol, thymol, or some such innocuous pre- 

 servative. 



Effects of temperature. Eennin is quickly destroyed in neutral solu- 

 tion by a temperature of 70 C., in acid solution by a temperature of 

 63 C. The temperature of maximum activity lies at 38 to 40 C. It 

 also acts, though more slowly, at atmospheric temperatures. 



Action of acids and alkalies. Eennin is rapidly destroyed by caustic 

 alkalies ; even O025 per cent, of caustic soda suffices, at atmospheric 

 temperature in twenty-four hours, to completely destroy a very active 

 solution. The amount of ferment so destroyed varies as usual with the 

 duration of the action, the temperature, and the concentration of the 

 destructive agent. In their behaviour towards alkaline carbonates 

 rennin and its zymogen closely resemble pepsin and pepsinogen ; rennin 

 being quickly destroyed by 0'5 to 1/0 per cent, of sodium carbonate 

 (Na 2 C0 3 ), while its zymogen is much less readily affected thereby. 2 



Eennin is destroyed by standing under alcohol, but this change occurs 

 more slowly than the corresponding one in the case of pepsin. 



Separation of pepsin and rennin. For the preparation of a pepsin 

 solution free from rennin, a gastric extract containing both enzymes is 

 submitted to digestion in - 3 per cent, hydrochloric acid for forty-eight 

 hours at 38 to 40 C. ; the rennin is completely destroyed. Hammarsten 3 

 utilises Briicke's principle of mechanical precipitation, for the preparation 

 of a rennin solution free from pepsin, in the following method. An acid 

 infusion of the gastric mucous membrane is neutralised with magnesium 

 carbonate, and enough neutral acetate of lead is added to completely 

 precipitate all the pepsin accompanied by a portion of the rennin. 4 The 

 nitrate is further precipitated by more lead acetate aided by ammonia, 

 and the precipitate is separated and decomposed by very dilute sulphuric 

 acid, so yielding a solution of rennin almost free from proteid. This 

 solution is then further purified by mechanical precipitation with 

 cholesterin. 



The final product so obtained produced no effect on a flock of fibrin 



1 Hammarsten, loc. cit. 



2 Langley, Journ. PhysioL, Cambridge and London, 1880-2, vol. iii. p. 287; Boas, Ztschr. 

 f. Jelin. Med., Berlin, 1888, Bd. xiv. S. 249. 



3 Loc. cit. 4 As tested by the inability of the nitrate to digest fibrin. 



