Thus we find ourselves, at present, in this position. After all that has been said and done to prove the wonderful prevalence of “germs” in the atmosphere, we are really still in the region of hypothesis--no further advanced than we were in the time of Bonnet and of Spallanzani, so far as it concerns the organisms which are all important--_Bacteria_. Neither these nor their germs have been shown to exist in any recognizable abundance in the atmosphere, and yet in most fermentations they are the first organisms which display themselves; whilst in many such fermentations _Bacteria_ alone occur. Nay more, even were they present in any great abundance, there is some reason to believe that the majority of them would exist as mere dead, organic particles--because _Bacteria_ are more than likely to be unable to resist anything like an extreme or prolonged exposure to desiccating influences. The first and essential data in support of M. Pasteur’s hypothesis must, therefore, be regarded as entirely unproved in respect to _Bacteria_--which are the most important of all organisms, in relation to the cause of fermentation and putrefaction. Without the aid of elaborate experiments, however, the evidence which the microscope can supply is capable of leading us to the conclusion that such search for atmospheric _Bacteria_ germs, was comparatively useless. If it can be shown that _Bacteria_ can arise in a fluid independently of _visible_ germs, then, obviously, any inquiries as to the nature of the visible contents of the atmosphere, can have only a very indirect bearing upon the question as to the mode of origin of these organisms. And yet by the aid of the microscope, as I have elsewhere stated, one can watch the appearance of almost motionless specks, more or less uniformly diffused through a motionless film of fluid, and can see them gradually develop into moving _Bacteria_ or into _Torulæ_. So that, where no _visible_ germs previously existed, visible particles of living matter develop, and more or less rapidly grow into distinct _Bacteria_. This may be best seen in a drop of a fresh and very strong turnip infusion, which has been filtered several times through the finest paper. The drop, placed in a live-box, should be flattened into a thin film by the application of the cover.