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colloidal suspension (gequollenen Zustande); third, that without 
the presence of a sufficient quantity of calcium phosphate rennin 
coagulation will not take place; fourth, that the caseinogen is so 
modified through the action of the rennin that in the presence of a 
certain quantity of a lime salt it can no longer remain in solution, but 
is precipitated as casein (Kase) or paracasein calcium phosphate; 
fifth, that as the result of the action of rennin, caseinogen (casein) 
is split into at least two new proteids, casein (der Kase) and whey- 
proteid (Molkeneiweiss). The former contains a relatively small 
quantity of calcium salts and is insoluble, the latter contains larger 
proportion of calcium salts and is easily soluble. Finally Ham- 
marsten held it to be highly probable that the rennin coagulation 
of milk is analogous in many respects to the coagulation of fresh 
milk by heat, which occurs at 130° to 150° C, and that in this regard 
the action of rennin is similar to other fermentations. According 
to Hammarsten, therefore, the rennin coagulation of milk resolves 
itself into two distinct phases: (1) the conversion of caseinogen a 
into paracasein in the presence of calcium salts, (2) the precipitation 
of paracasein from its solutions through the action of calcium salts. 
It will be observed that the second phase of the coagulation is inde- 
pendent of the action of rennin. 
These earlier researches by Hammarsten on the rennin coagula- 
tion of milk have been the point of departure for the greater number 
of subsequent investigations in this field, and his conclusions respect- 
ing this process have been the subject of a great deal of discussion. 
During recent years the rennin coagulation of milk has been studied 
by many observers. Among these may be mentioned Duclaqx, Cou- 
rant, Lorcher, Fuld, Laqueur, Loevenhart, and others. As the result 
of his studies on the rennin coagulation of milk, Loevenhart (13) recog- 
nized essentially three distinct phases of the process: (1) Transfor- 
mation of caseinogen into paracasein; (2) alteration or rearrangement 
of the mineral constituents of the milk, whereby the calcium salts be- 
come 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 avail- 
able 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 paracasein, 
is entirely independent of the action of the ferment. 
a The name caseinogen is employed throughout this communication on the rennin 
coagulation of milk in the sense in which it was first used Dy Halliburton (11), namely, 
as signifying the proteid of milk, which, through the action of rennin in the presence 
of certain calcium salts, is transformed into the casein (paracasein) of the curd. The 
term paracasein was first introduced into the science by Schulze and Rose (12) and 
is used in the sense employed by Hammarsten. 
