349 
closely approximates the condition of the caseinogen and phosphates 
as these substances exist in fresh milk. Whether these several 
substances are merely intimately mixed together or whether they 
form some loose chemical combination similar to a complex double 
salt can not be definitely determined at present. According to* 
Courant, however, all of these substances are necessary to the rennin 
coagulation, namely, dicalcium caseinogenate, soluble calcium 
salts, represented in the equation by monocalcium phosphate, and 
also tricalcium phosphate. According to this author only the dical- 
cium caseinogenate is altered in the rennin coagulation of milk, 
this being converted into paracasein. According to him the role 
of the soluble salts of the alkaline earths (calcium) in this process 
is simply to diminish the solubility both of the caseinogen itself and 
the paracasein. This last notion is in harmony with certain obser- 
vations by Ringer (40), who found that even fresh milk is coagulated 
by warming with small amounts of calcium salts. According to 
this author three drops of a solution of calcium chloride are sufficient 
to curdle ten cubic centimeters of fresh milk at 70° to 75° C. He 
further observed that while a very slight acidity seems, to favor the 
coagulation by calcium salts it is by no means essential to the process, 
since it can be brought about even in faintly alkaline milk. 
Finally, in the presence of soluble calcium salts the paracasein 
resulting from the action of rennin is precipitated in the form of an 
insoluble calcium salt containing calcium phosphate, either in loose 
chemical combination or as an intimate mixture. In this connection 
it has been shown by Harris (41) that in the curdling of milk by 
rennin 13 per cent more calcium phosphate is used up than in the 
acid coagulation of milk. 
In this connection Courant’s (42) views regarding the composition 
of milk and the manner in which the caseinogen is held therein afford 
the most satisfactory explanation of the conduct of fresh milk toward 
chemical indicators. To review this subject briefly, Courant has 
found that cow’s milk and caseinogen solutions, such as that whose 
composition is given in the above equation, react alkaline to lacmoid 
and acid to pkenolpkthalein. The acidity of fresh cow’s milk proved 
to be slightly less than that of the caseinogen solutions; the alkalin- 
ity of milk, on the other hand, was. nearly twice that of the caseinogen 
solutions. He reaches the conclusion that one half of the acidity 
toward phenolphthalein as shown by cow’s milk and his caseinogen 
solutions is due to the acidity of dicalcium caseinogenate, and the 
other half to monophosphates. In this calculation he purposely neg- 
lects the slight acidity of milk due 4o the free carbonic acid which 
it contains. The alkaline reaction toward lacmoid depends in the 
case of the caseinogen solutions partly on the dicalcium caseinogen- 
