347 
On the other hand, Laqueur (34) is inclined to question the validity of 
these conclusions. According to this author the weightiest objection 
that can be urged against these views is that at present we have no 
exact means of knowing whether the reaction resulting in the forma- 
tion of these plastein substances, as they have been called, is really 
the result of rennin action and whether we have a right to ascribe to 
these changes the same cause as that which brings about the conver 
sion of caseinogen into paracasein in the coagulation of milk. We 
know that as yet we have no means of operating with the pure fer- 
ment, but that in a solution of ferments the ferment itself often com- 
poses only a small part of the mixture, and in this connection it has 
been found that whereas one part by weight of the ferment solution is 
required to convert 48 grammes of albumose into plastein the same 
quantity of the ferment solution will convert from 10,000 to 100,000 
grammes of caseinogen into paracasein. Hence, according to Laqueur 
(34), it would seem to be a far-fetched conclusion to ascribe these two 
changes to the same ferment. It is therefore a mistake, according to 
this author, to assign to a ferment so widely distributed in plants and 
animals as that causing the plastein reaction a function absolutely 
identical with that of the ferment contained in the stomach of the calf, 
the latter producing the typical rennin coagulation of milk, until it 
has been definitely established that the ferment from plants, etc., also 
acts on caseinogen in two stages, in one of which calcium salts are 
required, and that the paracasein produced in the two processes is the 
same in each. Other chemists are also of the opinion that the plastein 
reaction is in reality due to pepsin and not to rennin at all. 
As a matter of fact the chemical and physical differences between 
caseinogen and paracasein are apparently so slight and in the pres- 
ent state of our knowledge so imperfectly understood that it is 
impossible to decide between all of these conflicting views on the 
rennin coagulation of milk. Laqueur (34) takes the stand that the 
hypothesis that rennin causes a coagulative splitting of caseinogen 
rests at least upon a foundation of fact, whereas the view that rennin 
exerts a synthetic action rests at present upon very deceptive analo- 
gies &nd 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- 
