THE GASTRIC JUICE. 143 



lead and tannic acid are without effect. Alcohol likewise precipi- 

 tates the ferment and gradually renders it inactive. Like pepsin, 

 it is not dialyzable. 



Under normal conditions chymosin is always present in the gastric 

 juice of man. In certain diseases of the stomach, however, which 

 are associated with the death of its glandular elements, the ferment, as 

 also its zymogen, is lacking. 



Tests for Chymosin and Chymosinogen. To test for the presence 

 of chymosin, 5 or 10 c.c. of milk are treated with a few drops of 

 the filtered gastric juice and kept at a temperature of from 37 to 

 40 C. If coagulation occurs within ten or fifteen minutes, the 

 presence of chymosin may be assumed. Should the gastric juice, 

 however, be markedly acid, it is necessary first to neutralize it with 

 barium carbonate. 



To test for chymosinogen, the milk is treated with 2-3 c.c. of a 

 1 per cent, solution of calcium chloride, and 10 c.c. of filtered 

 gastric juice which has been rendered feebly alkaline with sodium 

 hydrate. The mixture is kept at a temperature of from 37 to 40 

 C., when in the presence of the zymogen a thick cake of casein is 

 formed within a few minutes. 



Isolation of Chymosin. To isolate chymosin in comparatively 

 pure form, the following method, as suggested by Hammarsten, may 

 be employed : The mucous membrane of the fourth stomach of the 

 calf is carefully dissected off, washed with water, and extracted with 

 an 0.1 per cent, solution of hydrochloric acid, as already described. 

 The infusion is then neutralized and repeatedly shaken with 

 powdered magnesium carbonate until the pepsin has been removed. 

 The filtrate is treated with subacetate of lead, the precipitate 

 decomposed with very dilute sulphuric acid, and the acid filtrate 

 further precipitated with an aqueous solution of stearin soap. The 

 ferment is thus thrown down together with the fatty acids, from 

 which it is then separated by suspending the precipitate in water 

 and extracting the fatty acids with ether. The chymosin remains in 

 aqueous solution, and may now be precipitated with strong alcohol. 

 It is then rapidly collected on a filter and dried. 



Quantitative Estimation of Chymosin and Chymosinogen. As in 

 the case of pepsin and pepsinogen, relative values only can be 

 obtained. The gastric juice is neutralized with a very dilute solu- 

 tion of sodium hydrate. Tubes are then prepared, containing 5 or 

 10 c.c. of the gastric juice, variously diluted in the proportion of 

 1 : 10, 1 : 20, 1 : 30, etc., to which an equal volume of neutral or 

 amphoteric milk is further added. These tubes are kept at a 

 temperature of from 37 to 40 C., when the degree of dilution is 

 noted at which coagulation still occurs. Under normal conditions 

 a positive reaction can thus be obtained in man with a degree of 

 dilution varying between 1 : 30 and 1 : 40. 



In the case of the zymogen, the gastric juice is rendered feebly 

 alkaline, when tubes are prepared as just described. Normally a 



