8o THE BEGINNINGS OF LIFE. 



minute transplanted mass which takes root, skin grows 

 as from a centre, and the wound that was previously 

 intractable rapidly heals ^. 



But it may be asked, What is the cause or meaning 

 of this tendency shown by crystals and by different 

 kinds of living matter to mould suitable saline or 

 organizable materials into structures similar to them- 

 selves ? 



In the case of crystals, only one answer can be 

 given. There can be no reasonable doubt as to the 

 truth of the supposition that the form of the crystal is 

 a resultant necessity, predetermined by the molecular 

 properties of the matter which composes it, and the 

 sum total of conditions acting thereupon at the time of 

 collocation. That a crystalline structure once initiated, 

 therefore, should continue to grow in the same manner 

 in a solution of a suitable kind, is only to be ascribed 

 to the natural similarity of effect produced by uniform 

 forces acting under uniform conditions. And similarly^ 



^ This affords another instance illustrative of the fact that mere 

 growth can take place under conditions amidst which development or 

 evolution would cease. And, as Watts says (loc. cit., vol. ii. p. 115), 

 ' crystallization is also especially facilitated by introducing into the 

 liquid a crystal of the substances previously formed. A solution satu- 

 rated at a high temperature may, under certain circumstances, be cooled 

 down several degrees without depositing crystals ; but the introduction 

 of the crystal of a substance causes the whole to solidify instantly into 

 a crystalline mass. This phenomenon is easily exhibited with Glauber's 

 salt.' That this difference is only one of degree, however, is shown by 

 the fact that crystallization will take place spontaneously if the tempe- 

 rature be still further lowered. 



