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 converts 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 corpuscle. 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 m 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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