302 THE BEGINNINGS OF LIFE. 



the thick pellicle of the deep solution, whilst not a 

 single one appears in that which is shallow. Only one 

 mode of interpreting such facts seems possible. 



Lastly, it was long ago pointed out by Treviranus 

 and others, as we have before stated, that the kinds of 

 ciliated Infusoria met with in solutions varied with 

 the nature of the solutions themselves. This has since 

 been abundantly confirmed. M. Pouchet has shown 

 that different results are always to be obtained by 

 varying the organic substances, even when these are 

 exposed to the same air and dissolved in portions of 

 the same water ^ The amount of organic matter 

 existing in the solution will also influence not only 

 the rapidity of appearance, but even the kind of or- 



^ M. Pouchet says (' Nouvelles Experiences,' p. 127) : — ' Bory de Saint 

 Vincent, Trdviranus, Gerard, et Berard avaient assure d'apres leurs ex- 

 periences, que, quand on melait ensemble deux liqueurs fermentescibles 

 differentes, on obtenait de ce melange des etres organises qui differaient 

 de ceux que produisait chacune des liqueurs separees.' Again, he says : — 

 ' Beaucoup de substances organiques que nous denaturons pour nos be- 

 soins, donnent frequemment naissance a des productions speciales par- 

 faitement d^finies et qui ne croissent nuUe parte ailleurs. . . . Les Mucor 

 pygma'us et elegans ne se developpent que sur les aliments qui com- 

 men^aient a se putrefier et sur la colle seche ; le Spore?idonema casei ne 

 vit que sur le fromage ; le Chcetotnium chartarum sur les vieux papiers qui 

 s'alterent ; le Sporotrichum ruherrimum envahit le drap pourri ; le Torula 

 muralis n'a encore ete observe que sur les murailles recrepies. Qui 

 pourrait dire, ainsi que s'ecrie M. Fee qui a rassemble ces faits, oii etaient 

 les spores de ces vegetaux avant, que I'industrie humaine n'eut donne lieu 

 k ces produits?' (p. 183.) Hundreds of such facts might be cited, so 

 that, as M. Trecul suggests, if it were quite true that all these organisms 

 were derived from spores which pre-existed in the atmosphere, our 

 powers of locomotion might be to a certain extent impaired ! 



