105] DEAN—PROTEOLYTIC ENZYMES 133 
therefore, that the protoplasm of the cells starts the process of proteid 
decomposition, and carries it to some stage at which the ereptase 
takes up the work and completes the process. That the protoplasm 
has some hand in the process is made evident by the fact that killing 
the protoplasm is sufficient to stop the proteolysis, although the 
means taken are those which do not inhibit the action of enzymes. 
Moreover, when the cells of the cotyledons are placed under abnormal 
conditions, the hydrolysis of the proteids ceases. It is, of course, 
possible that the complete hydrolysis is carried out by the protoplasm 
and that the ereptase has no share in it. There is something to be 
said for either view. It might be pointed out that the ereptic activity 
as shown by the tissues of the cotyledons when acting on Witte 
peptone is quite sufficient to accomplish the ereptic part of the com- 
plete proteolysis. Moreover, the very fact that an enzyme is present 
which is capable of doing part of the work of cleavage would lead 
one to infer that it had some part to play in the process. On the 
other hand, it has been shown that the cotyledons contain relatively 
less ereptase than the ordinary vegetative organs, and that there is 
no increase, or at the most a very slight one, in the enzyme content 
during germination. 
The investigation of the other ograns of the plant shows that 
they all contain the ereptase in somewhat varying quantities, the 
roots containing the most per unit of nitrogen. There is no evident 
explanation for these quantitative variations, nor for the function 
of the enzyme in the metabolism of the cells. 
We have good reasons for believing that the life of every active 
cell is intimately bound up with a round of chemical changes of which 
part consists in a cleavage of the protoplasmic proteids. It is 
quite conceivable that the means by which the cleavage is effected 
may Vary in different cells; in some the whole process may be carried 
out by the protoplasm itself, unassisted by any of its enzymatic tools; 
other cells the protoplasm may start the process and split off 
Proteoses from itself which are subsequently attacked by an ereptic 
€nzyme and broken down to the amido-acids, hexon bases etc.; 
in still other cases it may be that the complete hydrolysis is carried 
Out by an enzyme or combination of enzymes. The bridging of the 
Sap between widely different forms by a series of small variations 
