ORIGIN OF LOWEST ORGANISMS. 23 



the agency of living ferments, we cannot receive hypo- 

 theses in evidence : facts are needed. These, no one 

 attempted to supply in an adequate manner * ante- 

 rior to the investigations of M. Pasteur. Speaking 

 of his researches, even M. Milne-Edwards says,t " Pre- 

 vious to this time, the existence of reproductive par- 

 ticles, or infusorial germs in the atmosphere was 

 nothing more than a plausible hypothesis, put forward 

 in order to explain the origin of such creatures in a 

 manner conformable with the general laws of repro- 

 duction ; but it was only a mere supposition, and no 

 one had been able actually to see or to handle these 

 reproductive corpuscles." 



We have to look, therefore, to M. Pasteur's investi- 

 gations, and to others which may have been since 

 conducted, for all the scientific evidence in support of 

 what has been called the " Panspermic hypothesis." 



By an ingenious method of filtration, which is fully 

 described in his memoir, J M. Pasteur separated from 

 the air that passed through his apparatus the solid 

 particles which it contained. This search convinced 

 him that there were, as he says, " constantly in ordi- 

 nary air a variable number of corpuscles whose form 



: M. Pouchet and others had examined the dust which settles 

 on objects, and amongst much debris of different kinds had found 

 comparatively few ova or spores. He had not, however, up to 

 this time, filtered the air, so as to see what germs might be 

 detected floating about in the atmosphere. 



f ' Anat. et Physiol. compar.' t. viii. p. 264. 



\ ' Annales de Chimie et de Physique,' 1862, t. Ixiv. p. 24. 



