THEORY OF THE CELLS. 209 
The following may be conceived to be the state of the matter : 
the material of which the cells are composed is capable of 
producing chemical changes in the substance with which it is | 
in contact, just as the well-known preparation of platinum | 
converts alcohol into acetic acid. This power is possessed by 
every part of the cell. Now, if the cytoblastema be so changed 
by a cell already formed, that a substance is produced which 
cannot become attached to that cell, it immediately crystallizes 
as the central nucleolus of a new cell. And then this con- 
verts the cytoblastema in the same manner. A portion of that 
which is converted may remain in the cytoblastema in solution, 
or may crystallize as the commencement of new cells ; another 
portion, the cell-substance, crystallizes around the central cor- 
puscle. The cell-substance is either soluble in the cytoblastema, 
and crystallizes from it, so soon as the latter becomes saturated 
with it; or else it is insoluble, and crystallizes at the time of 
its formation, according to the laws of crystallization of bodies 
capable of imbibition mentioned above, forming in this manner 
one or more layers around the central corpuscle, and so on. 
If we conceive the above to represent the mode of the formation 
of cells, we regard the plastic power of the cells as identical 
with the power by which crystals grow. According to the 
foregoing description of the crystallization of bodies capable of 
imbibition, the most important plastic phenomena of the cells 
are certainly satisfactorily explained. But let us see if this 
comparison agrees with all the characteristics of the plastic 
power of the cells. (See above, p. 194 et seq.) 
The attractive power of the cells does not always operate 
symmetrically ; the deposition of new molecules may be more 
vigorous in particular spots, and thus produce a change in the 
form of the cell. This is quite analogous to what happens in 
crystals ; for although in them an angle is never altered, there 
may be much more material deposited on some surfaces than 
on others ; and thus, for instance, a quadrilateral prism may be 
formed out of a cube. In this case new layers are deposited on 
one, or on two opposite sides of a cube. Now, if one layer in 
cells represent a number of layers in a common crystal, it may 
be easily perceived that instead of several new layers being 
formed on two opposite surfaces of a cell, the one layer would 
grow more at those spots, and thus a round cell would be elon- 
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