THEORY OF THE CELLS. 203 
and crystals, are, as we have observed, very different, even if 
we regard merely the plastic phenomena of the cells, and leave 
their metabolic power (which may possibly arise from some 
other peculiarity of organic substance) for a time entirely out 
of the question. 
Is it, however, possible that these distinctions are only 
secondary, that the power of crystallization and the plastic 
power of the cells are identical, and that an original difference 
can be demonstrated between the substance of cells and that 
of crystals, by which we may perceive that the substance of 
cells must crystallize as cells according to the laws by which 
crystals are formed, rather than in the shape of the ordinary 
crystals? It may be worth while to institute such an inquiry. 
In seeking such a distinction between the substance of cells 
and that of crystals, we may say at once that it cannot con- 
sist in anything which the substance of cells has in common 
with those organic substances which crystallize in the ordinary 
form. Accordingly, the more complicated arrangement of the 
atoms of the second order in organic bodies cannot give rise to 
this difference ; for we see in sugar, for instance, that the mode 
of crystallization is not altered by this chemical composition. 
Another point of difference by which inorganic bodies are 
distinguished from at least some of the organic bodies, is 
the faculty of imbibition. Most organic bodies are capable 
of being infiltrated by water, and in such a manner that it 
penetrates not so much into the interspaces between the ele- 
mentary tissues of the body, as into the simple structureless 
tissues, such as areolar tissue, &c.; so that they form an 
homogeneous mixture, and we can neither distinguish par- 
ticles of organic matter, nor interspaces filled with water. The 
water occupies the infiltrated organic substances, just as it is 
present in a solution, and there is as much difference between 
the capacity for imbibition and capillary permeation, as 
there is between a solution and the phenomena of capillary 
permeation. When water soaks through a layer of glue, we 
do not imagine it to pass through pores, in the common sense 
of the term; and this is just the condition of all substances 
capable of imbibition. They possess, therefore, a double 
nature, they have a definite form like solid bodies; but like 
fluids, on the other hand, they are also permeable by anything 
