350 
mucosa of the calf’s stomach has the power of curdling milk in both 
acid and alkaline solutions. To Hammarsten (10) and Schmidt (11), 
however, belong the credit of first showing that the rennin curdling 
of milk is accomplished by means of a soluble ferment to which they 
gave the name of “ labferment ” or “ chymosin.” This is the fer- 
ment which in English is called rennin, formerly rennet. Hammar- 
sten succeeded in showing: first, that the curdling of the milk by 
rennin is independent of the action of lactic acid; second, that the 
caseinogen (casein) of milk is not in true solution in milk but in 
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 a 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® 
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 coagulation 
of milk have been the point of departure for the greater number of 
subsequent investigations in this field, and his conclusions respecting 
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 Duclaux, Cou- 
rant, Lorcher, Fuld, Laqueur, Loevenhart, and others. As the result 
of his studies on the rennin coagulation of milk, Loevenhart (14) 
a The name caseinogen is employed throughout this communication on the 
rennin coagulation of milk in the sense in which it was first used by Hallibur- 
ton (12), namely, as signifying the proteid of milk, wdiich, 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 (13) and is used in the sense employed by Ham- 
marsten. 
