142 SCIENCE AND PRACTICE OF CHEESE-MAKING 



not exist as an uncombined protein, but is, accord- 

 ing to the best evidence available, in combination 

 with some form of calcium. Three general views 

 have been held in regard to the relation of calcium 

 (lime) compounds to milk-casein: (i) That 

 milk-casein is in the form of calcium casein, being 



j combined with about 1.50 per cent of calcium oxid; 



r. (2) that casein is combined directly with calcium 

 phosphate; (3) that the compound calcium casein 

 is also in combination with calcium phosphate. 

 Some facts appear to indicate that the calcium 

 casein of milk is a form containing 2.4 per cent of 

 calcium oxid. It has been well established that 

 casein forms compounds with calcium, but which 

 particular form of combination exists in milk, as 

 milk-casein, we cannot yet regard as settled beyond 

 question. 



Physical condition of casein in milk. — For a long 

 time casein was believed to be in solution in milk 

 and is still held to be so by those who have ignored 

 the evidence to the contrary. Some have held that 

 it was in a state of semi-solution. The view which 

 must now be regarded as representing the tfuth be- 

 ^•T^/if/yQj^^j all doubt is that casein exists in milk in the 

 form of extremely minute, gelatinous particles in 

 suspension. The evidence which proves the cor- 

 rectness of this view is threefold : ( i ) While the 

 solid particles of casein are so small that they easily 

 pass through the pores of fine filter-paper, they do 

 not go through the finer pores of unglazed porcelain 

 (like the Chamberland filter) nor through animal 

 membranes. It is thus possible to strain out casein 

 from the soluble portions of the milk in quantities 



