THE WONDERS OP LIFE 



solid crystalline form. We may, in a certain sense, call 

 this choice assimilation. In many crystals we can 

 detect internally an interaction of their parts. When we 

 cut off an angle in a forming crystal, the opposite angle 

 is only imperfectly formed. A more important difference 

 between the growth of crystals and monera is that the 

 former only grow by apposition, or the deposit of fresh 

 solid matter at their surface; while the monera grow, 

 like all cells, by intussusception, or the taking of new 

 matter into their interior. But this difference is easily 

 explained by their difference in consistency, the crystal 

 being solid and the plasm semi-fluid. Moreover, the 

 difference is not absolute; there are intermediary stages 

 between apposition and intussusception. A colloid 

 globule suspended in a salt solution in which it is not 

 dissolved may grow by intussusception. 



It was once the custom to restrict sensation and 

 movement to animals, but they are now recognized to be 

 present in nearly all living matter. They are, in fact, 

 not altogether lacking in crystals, as the molectdes move 

 in crystallization in definite directions, and unite accord- 

 ing to fixed laws; they must, therefore, also possess 

 sensation, as we could not otherwise understand the 

 attraction of the homogeneous particles. We find in 

 crystallization, as in every chemical process, certain 

 movements which are unintelligible without sensation — 

 unconscious sensation, of course. In this respect, also, 

 then, the growth of all bodies follows the same laws 

 {cf. chapters xiii. and xv.). 



The growth of a crystal is restricted like the growth 

 of a moneron or of any cell. If the limit is passed and 

 the conditions remain favorable to growth, we find an 

 instance of that excessive or transgressive growth which 

 we call reproduction in the case of living individuals. 

 But we find just the same kind of extension in the 

 inorganic crystal. Every crystal grows in a super- 



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