THE BEGINNINGS OF LIFE. 301 



the crystals, which separate out; and in the case of 

 those supersaturated solutions which crystallise suddenly 

 on exposure to the air, it is due to the presence of 

 minute particles of that salt floating in the air. From 

 an experiment of De Gernez it appears that micro- 

 scopic crystals of sodic sulphate may be obtained by 

 passing air, even in the open country, through pure 

 water, and evaporating the water on a glass plate. 

 Jeannel, however, denies the necessity of contact with 

 the salt actually contained in the solution. He finds, 

 indeed, that a supersaturated solution of sodic acetate 

 may be made to crystallise by contact with any solid 

 substance (a piece of paper, for example), and a solution 

 of sodic tartrate by contact with a clean, dry, glass 

 rod.' Here, then, we have a veritable c germ ' contro- 

 versy referrible to crystals. I have been informed, 

 however, by Prof. Frankland, that even in the case of 

 sodic sulphate it has been shown that, under certain con- 

 ditions^ crystallisation can take place where no crystal- 

 line germ could possibly have existed. 



The c germ' theory of the origin of crystals in 

 supersaturated solutions has, therefore, not only been 

 in existence, but has been overthrown. This has been 

 possible, however, only because it has been more easy 

 to show that a given set of conditions are inimical to 

 the existence of a crystal, than it has yet been to induce 

 people to believe that any given set of suitable experi- 

 mental conditions are incompatible with the existence 

 of matter in the living state. 



