36 ORIGIN OF LOWEST ORGANISMS. 



fessions concerning Bacteria, but also by the micro- 

 scopical evidence to which I have referred. 



So that in explaining the results of any experi- 

 ments made with the view of throwing light upon the 

 cause of fermentation or putrefaction, it is especially 

 necessary to bear in mind two considerations : 



I. That dust filtered from the atmosphere cannot 

 be proved to include living Bacteria; though it is 

 known to contain a multitude of organic particles 

 which may be capable in the presence of water, in ac- 

 cordance with Liebig's hypothesis, of acting as ferments. 



II. It must also be recollected that, in the opinion 

 of many, Life represents a higher function which is 

 displayed by certain kinds of organic matter ; and that 

 this higher function may be deteriorated or rendered 

 non-existent by an amount of heat which might not 

 be adequate to decompose the organic matter itself. 



It is all the more necessary to call attention to 

 these two considerations, because M. Pasteur invari- 

 ably speaks as though it had been established that 

 the air contains multitudes of living Bacteria, when, 

 really, he had only proved that the air contains a 

 number of corpuscles resembling spores of fungi, &c. 

 And, as I have already intimated, the existence of 

 spores of fungi in the atmosphere, however well 

 established, is of little or no importance as an ex- 

 planation of the cause of a very large number of 

 fermentations. Their presence is even of still less im- 

 portance, owing to the fact of the co-existence with 



