COAGULATING MATERIALS 35 



The presence of soluble calcium salts (or other alkaline 

 earth salts) seems to be essential, and the precipitate 

 formed is not casein or a casein salt, but a salt of a slightly 

 different nucleoalbumin called " paracasein." Many 

 writers, following Halliburton, call this modification 

 produced by rennin the " casein " and that from which 

 it is derived, " caseinogen." Foster and a few others 

 have used the term " tyrein " for the rennet clot. 



A number of investigations have been made on the 

 conditions essential or favorable to formation of the 

 coagulum, especially with regard to the effects of the 

 degree of acidity and of conditions affecting the amount 

 of calcium present, either as free soluble salt or bound to 

 the casein. Soluble salts of calcium, barium and stron- 

 tium favor or hasten coagulation, while salts of ammonium, 

 sodium and potassium retard or prevent coagulation. 



The bulk of the coagulum from milk is a calcium para- 

 caseinate, but it carries down with it calcium phosphate 

 and fat, both of which bodies have been helped to remain 

 in their state of suspension in milk by the presence of 

 the casein salt. Lindet (1912) has concluded that about 

 one-half of the phosphorus contained in the rennet curd 

 is in the form of phosphate of lime (probably tricalcic), 

 the other half being organically combined phosphoric 

 acid. 



52. Hammarsten's theory. According to Hammar- 

 sten (1877, 1896), whose view has been commonly held, 

 the distinctive effect of the ferment is not precipitation 

 but the transformation of casein into paracasein. This 

 is evidenced by the fact that if rennet be allowed to act 

 on solutions free from lime salts no precipitate occurs; 

 but there is an invisible alteration of the casein, for now, 

 even if the ferment be destroyed by boiling the solution, 



