COAGULATING MATERIALS 37 



casein with formation of paracasein. However, the 

 chemical and physical differences observed between casein 

 and paracasein appear to be so slight that Loevenhart 

 and some others think that they are only physical, per- 

 haps differences in the size of the colloid or solution 

 aggregates. Loevenhart conceives of a large part of the 

 work of the rennet (or of the acid, in acid and heat coagu- 

 lation) as being a freeing of the calcium to make it avail- 

 able for precipitation. Some think that the aggregates of 

 paracasein are larger than those of casein, but there is 

 more evidence of their being smaller, which idea cor- 

 responds with the findings of Bosworth, though he looks 

 on the change as a true cleavage. 



54. Bang's theory. Another description of the pre- 

 cipitation is given by Bang (1911), who studied the prog- 

 ress of the coagulation process by means of interruptions 

 at definite intervals. His observations confirm the idea 

 that rennin causes the formation of paracasein, and 

 that the calcium salt serves only for the precipitation of 

 the paracasein ; the rennin has to do also with the mo- 

 bilizing of lime salts. According to Bang, before coagu- 

 lation occurs, paracaseins with constantly greater affinity 

 for calcium phosphate are produced. These take up in- 

 creasing amounts of calcium phosphate, until finally the 

 combination formed can no longer remain in solution. 



55. Bosworth's theory. By a very recent work of 

 L. L. Van Slyke and A. W. Bosworth (Van Slyke and 

 Bosworth, 1912, 1913; and Bosworth and Van Slyke, 

 1913), in which ash-free casein and paracasein were com- 

 pared as to their elementary composition, and as to the 

 salts they form with bases, and the properties of these 

 salts, it is indicated that the two compounds are alike in 

 percentage composition and in combining equivalent, the 



