142 THE DIGESTIVE FLUIDS. 



noted, however, that calcium chloride or any other soluble calcium 

 salt is likewise capable of bringing about this result. The specific 

 action of chymosin is exerted upon milk or lime-containing solutions 

 of casein, which are coagulated in neutral and even feebly alkaline 

 solutions. Unlike pepsin, chymosin is not a proteolytic ferment, 

 and its action ceases with the formation of paracasei'n. It is there- 

 fore surprising to note that chymosin is found not only in the 

 stomachs of mammals, but also in other vertebrate animals, and 

 even in certain plants, where casei'n as a food-stuff certainly does not 

 enter into consideration. Our knowledge of ferments in general, how- 

 ever, is as yet very defective, and, as a matter of fact, we are acquainted 

 only with the more manifest reactions of these bodies, while it is 

 quite possible that they possess other important properties of which 

 we are now in ignorance. It is conceivable, moreover, that differ- 

 ent varieties of chymosin exist, which, as a class, are all capable 

 of coagulating casein, but w r hich differ from each other in other 

 respects and serve other purposes. 



The view of Pawlow and Parastschuk that pepsin and chymosin 

 are in reality one ferment and that coagulation and proteolysis are 

 merely different manifestations of the action of one ferment, has not 

 been generally accepted. 



The question has further been raised whether pepsin and chymo- 

 sin are the same in different animals or whether different varieties 

 of the ferments occur in different groups. While such differences 

 may exist, our knowledge of ferments generally is too defective to 

 warrant any definite statement either way. Bang has isolated a 

 parachymosin from calves 7 stomachs which is said to differ materi- 

 ally from that of man and the pig. 



While chymosin is also active in feebly acid solution, it is gradu- 

 ally destroyed at a temperature of from 37 to 40 C. when exposed 

 to the action of gastric juice containing 0.3 percent, of hydrochloric 

 acid. The ferment is here apparently digested by the pepsin, and it 

 is thus easily possible to obtain solutions of pepsin which are alto- 

 gether free from chymosin. In neutral solution it is more resistant, 

 and can be heated to a temperature of 50 C. ; at 70 C., however, 

 it becomes permanently inactive. In its dry state, on the other 

 hand, it can be heated to 110 C. without losing its activity. Alka- 

 lies when present beyond traces destroy the substance, as they do 

 pepsin. Like all other ferments, it is capable of effecting an exten- 

 sive reaction, even when present in small amount. The quantity of 

 ferment contained in 1 gramme of the dried and pulverized mucous 

 membrane of the fourth stomach of the calf, when dissolved in 

 water, is thus capable of coagulating 200 liters of milk in one 

 minute at a temperature of 50 C. 



Of the chemical nature of chymosin, nothing is known ; but, as 

 in the case of pepsin, the purer preparations do not give the usual 

 reactions of albumins. It is precipitated from its neutral solutions 

 by subacetate of lead, as also by uranyl acetate, while the acetate of 



