3O2 LIFE AND DEATH. 



stances more or less complete, in which its gems 

 appear simultaneously. This is what happens for 

 betol at about the temperatute of 10. These circum- 

 stances are those of the labile zone or zone of 

 spontaneous generation. 



Crystals of Glycerine. We may go a step further. 

 Let us suppose, with L. Errera, that we have a liquid 

 in a state of metastable equilibrium, whose labile 

 equilibrium is as yet unknown. This is what actually 

 occurs for a very widely known body, glycerine. 

 We do not know under what conditions glycerine 

 crystallizes spontaneously. If we cool it, it becomes 

 viscous ; we cannot obtain its crystals in that way. 

 It was not found in crystals until 1867. In that 

 year, in a cask sent from Vienna to London during 

 winter, crystallised glycerine was found, and Crookes 

 showed these crystals to the Chemical Society of 

 London. What circumstances had determined their 

 formation ? We knew not then, and we know not 

 now. It may be observed that this case of spon- 

 taneous generation of the crystals of glycerine has 

 not remained the solitary instance. M. Henninger 

 has noted the accidental formation of glycerine 

 crystals in a manufactory in St. Denis. 



It may be remarked that this crystalline species 

 appeared, as living species may have done, at a given 

 moment in an environment in which a favourable 

 chance combined the necessary conditions for its 

 production. It is also quite comparable to the 

 creation of a living species ; for having once appeared 

 we have been able to perpetuate it. The crystalline 

 individuals of 1867 have had a posterity. They 

 have been sown in glycerine in a state of superfusion, 

 and there they reproduced themselves. These 



