30 THE FLOATING-MATTER OF THE AIR. 



dered evident to the eye. The experiment proved that 

 no sensible amount of light was scattered by the rroole- 

 cules of the air ; that the scattered light always arose 

 from sxispeaded particles. The fact moreover that the re- 

 moval of these abolished simultaneously the power of 

 scattering light and of originating life, obviously de- 

 tached the life-originating power from the air, and fixed 

 it on something suspended in the air. Gases of all 

 kinds passed with freedom through the plug of cotton- 

 wool ; hence the thing whose removal by the cotton- 

 wool rendered the gas impotent, could not itself have 

 been matter in the gaseous condition. It at once 

 occurred to me that the retina, protected as it was, in 

 these experiments, from all extraneous light, might be 

 converted into a new and powerful instrument of demon- 

 stration in relation to the germ theory. 



The observations just described also revealed the 

 danger incurred in experiments of this nature ; showing 

 that without an amount of care far beyond that hitherto 

 bestowed upon them, such experiments left the door 

 open to errors of the gravest description. It was 

 especially manifest that the chemical method employed 

 by Schultze in his experiments, and so often resorted 

 to since, might lead to the most erroneous conse- 

 quences ; that neither acids nor alkalies bad the power 

 of rapid destruction hitherto ascribed to them. In 

 short, the employment of the luminous beam rendered 

 evident the cause of success in experiments rigidly con- 

 ducted like those of Pasteur ; while it made equally 

 evident the certainty of failure in experiments less 

 severely carried out. 



