1871.] The Theory of Atmospheric Germs. 161 



living molecules grow wherever they find a soil meet for 

 them, and in different soils develop into different forms, and 

 produce by their vital acts different effects. 



It now appears that none of the objections hitherto urged 

 are fatal to the germ theory. Chief, however, amongst the 

 arguments adduced against it has been that deduced from 

 the results of destructive agencies. 



At a very early period in the history of the controversy 

 concerning the origin of life, investigations were made 

 with the intention of determining this question. Can 

 vital organisms be found to develop under physical 

 influences which are, under ordinary circumstances, fatal 

 to any living thing ? If so, there is a great difficulty in 

 the way of accepting the germ theory. The heterogenists 

 have argued that living bodies are discovered after processes 



Fig. 7. 



«•*■» 



Fig. 6. ./fjL*7V: g 





Acetic ferment in course of 

 development. (Hallier.) 



Acetic ferment from the surface of stale beer. 



of physical destruction which it is impossible for life-pos- 

 sessing matter to withstand ; therefore, by exclusion, spon- 

 taneous generation must occur. 



The necessary conditions for experiments of this nature 

 are — (1) the subjection of fermentescible matter to such 

 destructive agencies that vitality in it is impossible ; (2) the 

 prevention of any subsequent contact with it of an agent 

 which may be a possible vehicle of vitality. 



The agency usually employed for the destruction of all 

 possible life in fermentescible fluids has been heat ; the pre- 

 cautions against the admission of possible germs or germ- 

 laden air have been various. The most simple of these 

 processes has been the subjection of the fermentescible fluid 

 to heat, varying in intensity in different experiments, and its 

 preservation in sealed flasks whence air was as rigidly 

 as possible excluded. The originator of this method of 

 investigation was Needham. Since his time it has been put 

 in practice with varying methods for the exclusion of possible 

 germs after the heating of the fluid. The temperatures 



VOL. VIII. (O.S.) — VOL. I. (N.S.) Y 



