SEP. / A'. / 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 he afterwards obtained by precipi- 
tating the glycerin extract with excess of alcohol, filtering, ami 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. — Rennin 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. — Rennin is rapidly destroyed by caustic 
alkalies ; even - 025 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 qiiickly destroyed by - 5 to TO per cent, of sodium carbonate 
(Na 2 C0 3 ), while its zymogen is much less readily affected thereby. 2 
Rennin 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 03 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 
filtrate 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, Joe. cit. 
• Langley, Joum. Physiol., Cambridge and London, 1880-2, vol. iii. p. 287 ; Boas, Ztschr. 
f. klin. Med., Berlin, 1888, Bd. xiv. S. 249. 
3 Loc. cit. 4 As tested by the inability of the filtrate to digest fibrin. 
