LIFE 



Schwann. It has been much criticised by recent cytol- 

 ogists, and does not hold in all respects. Still it is of 

 importance, as the crystal is the most ])erfect form of 

 inorganic individuality, has a definite internal structure 

 and outward form, and obtains these by a regular growth. 

 The external form of crystals is prismatic, and bounded 

 by straight surfaces which cut each other at certain 

 angles. But the same form is seen in the skeletons of 

 many of the protists, especially the flinty shells of the 

 diatomes and radiolaria; their silicious coverings lend 

 themselves to mathematical determination just as well 

 as the inorganic crystals. Midway between the organic 

 plasma-products and inorganic crystals we have the 

 bio-crystals, which are formed by the united plastic 

 action of the plasm and the mineral matter — for in- 

 stance, the crystalline flint and chalk skeletons of 

 many of the sponges, corals, etc. Further, by the 

 orderly association of a number of crystals we get com- 

 pound crystal groups, which may be compared to the 

 communities of protists — for instance, the branching 

 ice-flowers and ice-trees on the frozen window. To 

 this regular external form of the crystal corresponds a 

 definite internal structure which shows itself in their 

 cleavage, their stratified build, their polar axes, etc. 



If we do not restrict the term "life" to organisms 

 properly so-called, and take it only as a function of 

 plasm, we may speak in a broader sense of the life of 

 crystals. This is seen especially in their growth, the 

 phenomenon which Baer regarded as the chief character 

 of all individual development. When a crystal is formed 

 in a matrix, this is done by attracting homogeneous 

 particles. When two different substances, A and B, are 

 dissolved in a mixed and saturated solution, and a 

 crystal of A is put in the mixture, only A is crystallized 

 out of it, not B; on the other hand, if a crystal of B is 

 put in, A reraains in solution and B alone assumes the 



41 



