98 ORIGIN OF LOWEST ORGANISMS. 



mere addition of those portions of unstable organic 

 matter, whose molecular mobility has not been impaired 

 by the agency of heat, and which are therefore capable 

 of initiating fermentations. This view is strengthened, 

 as M. Pouchet has pointed out, by the fact that in 

 these cases, instead of meeting some of the various 

 kinds of organisms which are supposed to have repre- 

 sentatives in the air, and whose spores or ova may be 

 supposed to have been sown, it is often merely Bac- 

 teria which are encountered, differing in no respect 

 from those that may present themselves in a some- 

 what similar infusion, which has undergone change 

 in a closed flask without any such hypothetical sowing 

 of living spores or germs. It is more especially im- 

 portant to bear in mind this consideration, when por- 

 tions of organic matter can always be easily demon- 

 strated amongst such atmospheric dust ; whilst living 

 Bacteria, or other organisms, such as are first produced 

 as a result of the supposed sowing of spores, either 

 cannot be demonstrated, or would seem, from other 

 evidence, to be at least very sparingly distributed.* 



The fact revealed by M. Pasteur, that some fluids 

 remain unchanged for an indefinite period, after having 

 been boiled in flasks, with long and bent necks, is 

 easily explicable in accordance with the physical 

 theory of fermentation, and now that it has been 

 thoroughly proved that other fluids submitted to pre- 



* On what other supposition can one explain the results of 

 experiments LVII.-LXV., and of others alluded to on p. 100? 



