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recognized essentially three distinct phases of the process : (1) Trans- 
formation of caseinogen into paracasein; (2) alteration or rearrange- 
ment of the mineral constituents of the milk, whereby the calcium 
salts become available for the coagulation; (3) precipitation of the 
paracasein by calcium salts. He has shown that the conversion of 
caseinogen into paracasein proceeds somewhat more rapidly than the 
rendering available of the calcium salts. According to this author 
the first two phases of the process are accomplished by the action of 
rennin, whereas the third phase, namely, the precipitation of the para- 
casein, is entirely independent of the action of the ferment. 
He also arrived at the conclusion from his study of the infiuence of 
salts on the coagulation of decalcified milk that the facts observed 
seemed to favor the theory that the curdling of milk depends in great 
part, though not entirely, on the rearrangement or rendering availa- 
ble of its mineral constituents. He succeeded in showing that fresh 
milk can not precipitate paracasein solutions nor can it prevent their 
precipitation by calcium chloride. Hence it would seem that the 
calcium salts of fresh milk are in some way altered through the action 
of rennin, thereby becoming capable of precipitating paracasein. 
He concludes therefore that in the rennin coagulation of milk the 
rennin has the power in some way to render available the calcium 
salts (die calcium Salze frei zu machen), since without this change 
no coagulation is possible. Similarly Briot (15) maintains that 
rennin acts less on the caseinogen than on the calcium phosphate of 
milk. \Vhile this extreme view is probably incorrect it is certain that 
the majority of chemists are agreed regarding the necessity of cal- 
cium salts for the rennin coagulation of milk. That such is the case 
is evident not only from the earlier investigations of Hammarsten 
but also from later and more exact observations by Arthus and Pages 
(16), Courant (IT), Einger (18), Loevenhart (14), Edmunds (19), 
Benjamin (20), Soldner (21), Laqueur (22), and others. 
It has also been established by the work of Courant (17) that the 
reaction of milk is not altered during the rennin coagulation. 
The question still remains to be considered, How does the rennin 
act on the caseinogen and in what way is the latter altered through 
the action of the ferment? These questions have been exhaustively 
considered by Laqueur (23), who has arrived at the conclusion that 
from the slight differences between caseinogen and paracasein thus 
far made out it is impossible to arrive at an unequivocal explana- 
tion of the coagulation of milk by rennin. This author is inclined 
to believe, however, that Hammarsten’s original explanation of the 
process is perhaps, all things considered, the best we have. Accord- 
ing to this explanation the rennin acts by splitting the caseinogen 
into a larger molecule, paracasein, and a smaller molecule, the whey- 
proteid (molkeneiweiss) , also called hemicaseinogen albumose (Arthus 
