Rennet. 37 



1. The chemical reaction of rennet is hastened by the distri- 

 bution of the rennet and its quantitative relation to the casein, pos- 

 sibly also by elevated temperatures up to an unknown limit. Alka- 

 line earths and acids probably act in a similar manner by activat- 

 ing the rennet. 



2. The chemical reaction is retarded : (a) By the destruction 

 of the rennet: temperatures over 41 C., free hydroxylions ; (b) by 

 inactivation of the same: anti-rennet; (c) by changes of tho 

 casein : temperatures over 80 deg. ; formalin. 



3. The physical reaction is hastened by higher temperatures, 

 free hydrogenions, and the neutral salts up to a certain concentra- 

 tion, especially the salts of alkaline earths. 



4. The physical reaction is retarded by reducing the concen- 

 tration of the mentioned salts below a certain point, especially of 

 the alkaline earths ; therefore heating the milk and the salts which 

 precipitate lime, and calciumions will produce this result. Higher 

 concentrations of neutral salts have the same effect. It may also be 

 possible that some of the alkaline action should be considered here. 



It is known that by the injection of rennet into an animal an 

 anti-rennet may be produced. The rennet acting as antigen 

 induces in the body of the rabbit the formation of a specifically 

 acting anti-body, which works against the action of the antigen in 

 the re-agent glass, very likely through fixation. Normal serum 

 also contains rennet-inhibiting substances. 



The action of the rennet may be inhibited or entirely prevented by the addition of 

 horse blood as has been proved by Hammarsten, and later by Roden. The same inhibi- 

 tion is exerted on the action of trypsin and pepsin and is referred to as an anti-ferment 

 action of the blood serum. Blood of cattle added to cow's milk also shows this char- 

 acteristic (Schern). Inhibition action is traced back to the anti-ferment substances of 

 a specific nature contained in the blood, and the presence of an anti-rennet is considered 

 probable. It should however be noted that Eaudnitz and Jakoby prevented inhibition 

 by neutralizing the serum with acid. 



The strength of the rennet may be tested in various ways. 

 That quantity of milk is measured which is coagulated by one part 

 of rennet in 40 minutes at 35 deg. Market rennet has a strength 

 of 1:10,000 to 1 :100,000 (fluid rennet and solid rennet). 



Meunier ascertains the quantity of milk which is coagulated by one c. c. of undi- 

 luted gastric juice in ten minutes. Schern employs solutions of rennet (standard rennet 

 prepared according to Morgenroth) of varying density (1:100:200:300, etc). One part 

 of these rennet dilutions is mixed with nine parts of milk, so that milk-rennet dilutions 

 of 1:1000:2000:3000, etc. are obtained. After an action of two hours the samples are 

 placed in the incubator. The dilutions in which coagulation may now be demonstrated 

 give the relative value of the rennet for the respective milk, and if a mixed milk of 

 healthy animals had been used it establishes the " rennet-titer. " 



It is to be regretted that the standard rennet solutions are not 

 constant, and that they weaken by storing, etc. For this reason it 

 is necessary to establish the rennet-titer before each test on the milk 

 of healthy animals, or on casein solutions. 



In addition to the rennet of calves, extracts and ferments from other organs of these 

 animals act on milk in a similar manner, such as extracts of spleen, kidney, liver, lung, 

 thymus, intestine, ovaries, testicles and muscles. Rennet from the stomach of a calf is 

 known as chymosin ; rennet from the stomach of a hog, and from the gastric juice of man 

 as parachymosin (Bang). Rennet enzymes may also be demonstrated in the bodies of 

 other animals, fish, birds and snails. 



