COAGULATING FERMENTS 



417 



Cf. Chap. VI) by calcium salts or other salts of the alkaline 

 earths. The part played by calcium in forwarding the coagu- 

 lation of blood is very different; here the dependency is one 

 of the ferment (or a pro-ferment), and not of the coagulation 

 of the substrate, upon the presence of calcium salts; it would 

 appear that calcium salts activate a pro-thrombin, converting it 

 into the ferment thrombin, which will then induce coagulation 

 whether calcium salts be present or not. The function of cal- 

 cium in these two processes is therefore very different. 



Fuld (32), Gerber (37) and Madsen (77) have shown that for 

 the coagulation of milk by rennet F X t = constant; i.e., the 

 velocity of coagulation is proportional to the concentration of 

 ferment. Regarding the influence of calcium salts, very inter- 

 esting results have been obtained by Reichel and Spu'o (104). 

 These observers added to 8 cc. of milk different quantities (R) 

 of rennet solution and different amounts (p) of calcixmi chloride, 

 and diluted with water to a total volume of 100 cc. They then 

 measured the time required for coagulation at a constant tem- 

 perature. The following were their results : 



It is evident that the product (p -f- 0.6) i is constant for each 

 value of R, provided p does not exceed 2 per cent. The velocity 

 is also proportional to R, so that the complete relationship is 

 R{p -\- 0.6) t = constant. The quantity 0.6 which must be added 

 to p in the above equation is to be regarded as the (percentage) 

 concentration of calcium ions present already in milk, before 

 any calcium chloride is added. According to Reichel and Spiro 

 this indicates that only about 15 per cent of the calcium in milk 



