Crystals obey the principle of Heredity. 1 1 1 



form of crystal only produces crystals of like form and 

 property (or at most in certain cases a limited number 

 of modified forms, as in the instance of calcic car- 

 bonate, &c.) so also each seed, both of animals and 

 vegetables, only produces its own particular essential 

 shape and collection of functions. The same principle 

 shews itself in the transmission of particular types of 

 disease, and of eccentricities of organization, from one 

 generation to another of animals. Peculiar malfor- 

 mations of body and characteristics of mind often 

 persist in families from generation to generation. 

 This persistency or heredity of structure and of 

 property is not limited to solid bodies, but exists also 

 in liquids : " The effect of vaccine virus upon the 

 liquid blood, in producing a permanent and organic 

 change in its constitution and character, which con- 

 tinues to exercise a protective influence against 

 small-pox, in the great mass of cases, through a long 

 life, during which time the blood must have under- 

 gone, many thousands, if not millions of changes and 

 modifications." (F. Winslow. "Obscure diseases of 

 Brain and Mind," page 432). The same persistency of 

 structure and property of structure, has even been 

 detected in vapours ; the vapour of red iodide of 

 mercury for example, deposits only crystals of red 

 iodide, whilst that of the yellow deposits only yellow 

 {see Gmelin's Handbook of Chemistry, vol. I, p. 100.) 

 We often appear to mentally select when we only 

 yield to causes acting upon us, i.e. t to the strongest 

 influence or motive. That " self-preservation is the 



