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coagulation of milk. Laqueur (23) takes the view, however, that 
the hypothesis that rennin causes a coagulative splitting of caseino- 
gen rests at least upon some foundation of fact, whereas the view 
that rennin exerts a synthetic action rests at present upon very 
deceptive analogies and teleological evidence. 
The more one studies the extensive literature of the rennin coagu- 
lation the more one is disposed to agree with Laqueur that in the 
present state of our knowledge it is impossible to arrive at an une- 
quivocal explanation of this complicated process. It seems, how- 
ever, to have been reasonably well established — 
(1) That, exclusive of phosphates of calcium and other soluble 
salts of calcium, caseinogen is the only substance in milk involved 
in the rennin coagulation. 
(2) That in the rennin coagulation of milk no change of reaction 
occurs; that is, no production of base or acid. In this connec- 
tion it has been pointed out by Herwerden (31) that hydrogen ions 
are not necessary for the rennin coagulation of milk or of solution 
of caseinogen containing calcium. 
(3) That in the rennin coagulation of milk two active agents are 
concerned, a soluble ferment, rennin, and calcium ions; that is, solu- 
ble calcium salts. 
According to Hammarsten the caseinogen is resolved by rennin 
into paracasein and whey proteid. Through the action of calcium 
ions (soluble calcium salts), the former is then precipitated as the 
curd (Kase), the latter remaining in solution. According to Fuld 
and others the change of caseinogen into paracasein is a molecular 
rearrangement. According to Courant the dicalcium caseinogenate 
is so altered by rennin that by contact with soluble calcium salts a 
precipitate (the curd) is produced. According to Lovenhart the 
rennin renders the calcium salts of milk available for the coagulation 
of paracasein, which latter is formed from caseinogen also by the 
action of rennin, and which, according to this author, differs from 
caseinogen only in that it is composed of larger molecular aggregates. 
It will be observed that these several views regarding the precise 
mode of action of the rennin differ in some particulars. These dif- 
ferences can only be reconciled by further investigation. 
It has been shown by Soldner (32), Osborne (33), Courant (IT), 
and others that caseinogen is an acid. According to Courant it forms 
three kinds of salts, namely, mono-, di-, and tri-caseinogenates. It 
also seems probable from Lehmann’s (1) investigations that the 
caseinogen exists in fresh milk in the form of a complex calcium 
salt containing calcium phosphate. According to this author the 
