THE BEGINNINGS OF LIFE. 297 



duction, therefore, will not adequately account for the 

 thousands of ciliated Infusoria which are often to be 

 met with in the course of a few days in many organic 

 infusions; and moreover, as long as we are able to 

 demonstrate that Fungus-spores, Monads, Amoebae, and 

 Ciliated Infusoria are constantly produced by changes 

 taking place in a pellicle, or living stratum formed by 

 aggregations of Bacteria, it is perfectly immaterial 

 whether the air does or does not contain any of these 

 higher organisms or their germs. 



Again, in the face of what we know concerning the 

 paucity with which ciliated Infusoria and the micro- 

 scopic Fungi of infusions are represented in the atmo- 

 sphere, concerning the extreme rarity of the sexual 

 method of reproduction amongst Infusoria, and also as 

 to the comparative infrequency with which multipli- 

 cation by fission can be observed, the results afforded 

 by comparisons of cases in which there has been free 

 exposure either of different solutions to the same air, or 

 of portions of the same organic solution under different 

 conditions, are also strongly opposed to the notion of 

 the derivation of such organisms from pre-existing 

 atmospheric germs. The evidence thus obtainable, 

 however, tallies remarkably with the notions of hetero- 

 genists as to the principal mode of production of these 

 organisms being from the very substance of the pellicle 

 itself. 



If the higher organisms met with after a time in 



