RENNET AND ITS PROPERTIES. 207 



temperature of 35 C., in 40 minutes. This is best carried out 

 as follows: 5 c.c. of the rennet solution which it is desired to 

 test, or a watery solution in which 5 grams of the rennet powder 

 is dissolved, are made up to 100 c.c. with distilled water. After 

 thorough mixing, 10 c.c. representing '5 c.c. or '5 of a gram of 

 the rennet preparation is drawn off with a pipette and added to 

 500 c.c. of milk possessing an acidity of 7, which is then heated to 

 exactly 35 C. The exact time to a second is noted when this takes 

 place. The solution of rennet is blown with considerable force from 

 the pipette into the milk, in order that it may be uniformly distri- 

 buted throughout the mass, which is quickly submitted to a rotatory 

 motion. As is obvious, there will be one part of rennet for every 

 1000 parts of milk, that is, 1 c.c. or 1 gram of rennet per 1000 c.c. 

 of milk. The thermometer, which has been already placed in the 

 milk, is then gently moved to and fro, and the time noted which 

 elapses till coagulation becomes apparent, that is, till fine particles 

 of coagulated milk are apparent behind the thermometer as it is 

 moved as carefully as possible. The temperature of the milk must 

 be maintained during the whole operation as nearly as possible at 

 35 C. If, for example, the coagulation period has been observed to 

 last 5'55 minutes, then the quantity of milk (x) which would be 

 coagulated at the same temperature by a similar quantity of rennet 

 in 40 minutes' time is as follows: 



5'5 : 40 :: 1000 : x = 7207. 



The rennet preparation is thus found to possess a strength of 

 1 : 7207, or, roughly speaking, 1 : 7200. 



The commercial solutions contain, in addition to rennet ferment, 

 small quantities of pepsin, a non-organized ferment which produces 

 lactic acid, comparatively large quantities of slimy matters, and other 

 organic substances, the composition of which is little known. They 

 contain salt or alcohol, and often also other preservatives, such as 

 boracic acid, glycerin, ethereal oils, thymol, salicylic acid, benzoic 

 acid, &c. All these substances increase the keeping property of 

 the rennet solutions at the expense of their strength, since they 

 render a portion of the rennet ferment inactive. 



Rennet powders, on account of the method of their preparation, 

 are richer in the ferment and poorer in pure organic substances 

 than the pure commercial solutions of rennet. They are obtained, 

 as a rule, by separating and drying the precipitate prepared by 



