26o CLASSICS OF MODERN SCIENCE 

 this important point, that solid bodies of a certain regular shape are 

 formed in obedience to definite laws at the expense of a substance 

 contained in solution in a fluid ; and the crystal, like the cell, is so far 

 an active and positive agent as to cause the substances which are pre- 

 cipitated to be deposited on itself, and nowhere else. We must, there- 

 fore, attribute to it as well as to the cell a power to attract the sub- 

 stance held in solution in the surrounding fluid. It does not indeed 

 follow that these two attractive powers, the power of crystallization — 

 to give it a brief title — and the plastic power of the cells, are essen- 

 tially the same. This could only be admitted, if it were proved that 

 both powers acted according to the same laws. But this is seen at the 

 first glance to be by no means the case : the phenomena in the forma- 

 tion of cells 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 peculiar- 

 ity 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 ordi- 

 nary 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 consist in anything 

 which the substance of cells has in common with those organic sub- 

 stances 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 chemi- 

 cal composition. 



Another point of difference by which inorganic bodies are dis- 

 tinguished 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 elementary 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- 



