RENNIN. 475 



The law given on page 58 in which the time of coagulation is 

 inversely proportional to the amount of enzyme, is true for calf rennin 

 (FuLD x ) and for sheep rennin (HEDiN 2 ). The other rennins investi- 

 gated do not follow this law at 37 C., which, according to VAN DAM, is 

 due in the case of the pig rennin to its less resistance toward the alkali 

 of the milk. 3 



Rennin is just as difficult to prepare in a pure state as the other 

 enzymes. The purest rennin enzyme thus far obtained did not give the 

 ordinary protein reactions. On heating its solution rennin is more or 

 less quickly destroyed, depending upon the length of heating and upon 

 the concentration. If an active and strong infusion of the gastric mucosa 

 of the calf's stomach in water containing 3 p. m. HC1 is heated to 40-45 

 C. for 48 hours, the rennin or nearly all, is destroyed, while the pepsin 

 remains. A pepsin solution free from rennin can be obtained in this 

 way. 



A much-discussed question, is, whether the digestion of protein and 

 the rennet action are brought about by two special enzymes, or represent 

 two different enzyme actions, or whether there is only one enzyme, the 

 pepsin, which has both actions. The supporters of this last view dispose 

 of the question in different ways. Some, like PAWLOW and PARAST- 

 SCHUK, consider the rennet action simply as the reverse of the synthetical 

 action of pepsin, a view which is improbable in the highest degree. 

 Others, such as SAWJALOW 4 and GEWIN, consider, on the contrary, that 

 the coagulation of milk is only a pepsin action and indeed as the first 

 step in the beginning of proteolysis, namely, the beginning of peptic 

 digestion of casein. ROKOCZY 5 believes in the presence of two enzymes 

 in the calf's stomach, one of which, the rennin, disappears on the increas- 

 ing age of the animal. 



The simultaneous occurrence in the animal and plant kingdoms of 

 enzymes having a proteolytic and rennet action and the parallelism of 

 the pepsin and rennet action indicates an identity of both enzymes and 

 enzyme actions. This parallelism in fact does not prove much, because 

 it has mostly been studied in acid reaction, while rennet is character- 

 istically active in neutral or faintly alkaline reaction. 



At the same time HAMMARSTEN 6 finds that in acid reactions no 



1 Hofmeister's Beitrage 2. 



2 Not published investigations. 



3 Zeitschr. f. physiol. Chem. 64, 316 (1910). 



4 The recent literature on this question can be found in Hammarsten, Zeitschr. 

 f. physiol. Chem., 56, 18 (1909). 



5 Ibid. 68, 421 (1910), 73, 453 (1911). 



6 Zeitschr. f. physiol. Chem. 68, 119 (1910), which also contains the recent literature. 



