THE STRUCTURE OF PROTOPLASM 29! 
faces formed between them as phases of a colloidal system. The slowness 
of the diffusion of colloidal ferments leads to their becoming rooted as it 
were in certain regions of the cell most favorable for their activity. 
No one can deny that this picture of the chemical organization of the 
cell does full justice to many of the observed facts of cytology as well as 
to the processes of physiological chemistry. The conception of the enzyme 
is perhaps over-emphasized in view of the slight knowledge which we have 
of the chemical nature of these elusive compounds. But the localization 
of functions in the cell and the special acceleration of certain general reac- 
tions in particular regions of the cell are conceptions which can be connected 
directly with the cytology of starch formation, oil formation, the building 
of astral rays, spindle fibres, and cilia, the production of cell pigments, etc. 
Hofmeister does not at all emphasize the phase relations of these various 
constituents of the cell, and it is obvious that a polyphase colloidal system 
does not of itself involve such structural differentiations as Hofmeister 
assumes and the microscope reveals. No matter how great the number of 
phases or how intimate their interrelations are assumed to be, the polyphase 
system in itself might be in general homogeneous throughout its whole 
extent, that is, the particular phases and their interrelations might repeat 
themselves in all directions through the mass in a uniform and undifferen- 
tiated sequence. That is, just as in a two-phase system any one unit 
area large enough to include the two phases will be essentially like any other 
unit area of equal size in the mass, so in the polyphase system the mass is 
naturally conceived as including an indefinite number of repetitions of unit 
areas essentially alike as to their makeup. The polyphase system is merely 
the two-phase system increased as to the number of its constituent elements^ 
It is only by adding the conceptions of zonation and other types of segre- 
gation of the elements of the polyphase system due to their chemical inter- 
relations that we arrive at a parallelism with what is seen in the cell. 
We can put this in another way which will at once bring out the pecu- 
liarities of cell organization as compared with polyphase systems in vitro 
by noting that the polyphase system may be homogeneous in the respect 
that it shows no axial differentiation. Whatever the interrelations of the 
phases as to internal and external, sol or gel, they will be the same at the 
top as at the bottom, in the front as at the rear, on the right side as on the 
left side. The only exception is that any polyphase system will differ on 
its surface as compared with its interior, that is, will show some concentric 
zonation. This difference has been exploited to the full in the numerous 
recent attempts to utilize the data of colloid chemistry in the analysis of 
the structure and functions of the plasma membrane. It would take us too 
far afield to review the data in this complicated subject further than to 
note that none of the theories — lipoid, mosaic, adsorption, filter, etc., have 
contributed anything very positive to the general theories of protoplasmic 
structure. 
