353 
stances, comes to exactly the opposite conclusion, viz, that caseinogen 
is probably a higher colloid than paracasein. 
According to Laqueur (23), the idea that paracasein is a more com- 
plex substance than caseinogen has also received support from 
Danilewski's observation that rennin gives rise to a precipitate in 
solutions of albumoses. According to the Kussian investigators, by 
whom this reaction has been extensively studied, this precix^itate pos- 
sesses the properties of a higher proteid. They therefore see in this 
change the synthesis of a complex substance having the nature of 
naturally occurring proteids from the products of assimilation, and 
find a ready explanation for the widespread occurrence of rennin in 
the tissues of animals and plants which are in no wise concerned with 
the digestion of milk. On the other hand, Laqueur (23) 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 wdiether the 
reaction resulting in the formation 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 conversion of caseinogen into paracasein in 
the coagulation of milk. We know that as yet we have no means of 
operating with the pure ferment, but that in a solution of ferments 
the ferment itself often composes 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 para- 
casein. Hence, according to Laqueur (23), 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 im- 
possible to decide between all of these conflicting views on the rennin 
45276°— Bull. 56—12 23 
X 
