148 



THE MILK-CURDLING ENZYME. 



[BOOK II. 



One of the most interesting facts connected with 

 the composition of the gastric juice of man, and which 

 deserves to be brought into much greater prominence 

 than has been usual, is that in the adult human subject 

 in a state of health the rennet ferment is never absent 

 in the physiological condition. It is only in cancer, 

 atrophy of the mucous membrane of the stomach, and in 



The milk- 

 curdling fer- 

 ment a con- 

 stant ingredi- 

 ent of Human 

 Gastric Juice. 



in 



chronic gastric catarrh, that it has been found absent. 



The mucous membrane of the stomach of the calf 

 and of the sheep always contains ready-formed milk- 

 curdling ferment, which can be extracted from it by 

 the action of water and other solvents to be men- 

 tioned hereafter; most frequently none can be ex- 

 tracted by water from the mucous membrane of the 

 stomach of other mammals or of birds, and it is 

 scarcely ever present in that of fishes. 



Although the free ferment removeable by water is rarely found, 

 Hammarsten has shewn that the gastric mucous membrane of all 

 animals in which it has been investigated, without exception, contains 

 a body which is not the milk- curdling ferment, but its zymogen: from 

 this the milk-curdling ferment is quickly liberated on the addition of 

 an acid. 



The milk- 

 curdling en- 

 zyme or its 

 zymogen re- 

 side in the 

 gastric mu- 

 cous mem- 

 brane of cer- 

 tain animals. 



Distribu- 

 tion of the 

 milk-curd- 

 ling enzyme 

 in the mucous 

 membrane of 

 the stomach. 



Hammarsten has found that the mucous membrane 

 of the fundus is very much richer in the milk-curdling 

 ferment and its zymogen than that of the pylorus. So 

 far as experiments have been made, variations in the 

 amount of rennet ferment (including rennet-zymogen), 

 in the gastric mucous membrane, run parallel with 

 variations in the amount of pepsin (including pepsinogen). Probably 

 rennet-zymogen, like pepsinogen, takes its origin in the granules of 

 the chief cells. 



Mode of Although the mucous membrane of the stomach of 



paring 6 an 'ac- *he calf and of the sheep always yields to water havin< 

 tive solution of a neutral reaction a sufficient quantity of milk-curdling 

 the ferment ferment to demonstrate its peculiar properties, mucl 

 and of observ- more powerfully-acting solutions are obtained by th< 

 s action. a ^ ^ dilute acids, as follows : The mucous membram 

 of the stomach, preferably of a calf, is digested for 24 hours, at ordi- 

 nary temperatures, in 150 200 c.c. of very dilute hydrochloric 

 acid, containing from O'l to 0'2 per cent, of HC1. The liquid is 

 then filtered and carefully neutralized. Twenty-five c.c. of fresh milk 

 are then heated to 38 C., and treated with 1 c.c. of the neutralized 

 liquid. Curdling is induced within a period of two minutes ; this 

 occurs even if the milk have been rendered faintly alkaline by caustic 

 soda; the alkaline reaction persists after curdling. A glycerin- 



