[16] Those which he believed to be eggs of ciliated infusoria, may be at once dismissed from consideration, as we are not at present concerned with the origin of organisms of this kind. [17] _Loc. cit._ p. 34, note ^{1}. But another most important consideration presents itself. M. Pasteur’s researches as to the nature of the dust contained in the atmosphere enable him to say nothing concerning the presence of _Bacteria_, although he himself admits that these are generally the first organisms which display themselves in fermentations or putrefactions, and that in a very large majority of the cases in which fermentation occurs in closed vessels they are the only organisms which make their appearance.[18] And yet, notwithstanding these facts, M. Pasteur says, in reference to the common form of _Bacterium_:--“This infusorial animal is so small that one cannot distinguish its germ, and still less fix upon the presence of this germ, if it were known, amongst the organized corpuscles of the dust which is suspended in the air.” [18] _Loc cit._ p. 56. Here, then, we have a confession from M. Pasteur himself, that all evidence fails, where it is most wanted, in support of his hypothesis. If a large number of fermentations begin with the presence of _Bacteria_ as the only living things, and if in a number of cases no other organisms ever occur, it is useless to adduce as evidence, in proof of the view that fermentations are _always_ initiated by air-derived organisms, the fact that certain corpuscles (supposed to be spores of fungi) are recognizable in the atmosphere--capped by the distinct statement[19] that _Bacteria_ or their germs are not recognizable. If _Bacteria_ are not recognizable in the atmosphere, what scientific evidence is there that the fermentations in which these alone occur are initiated by _Bacteria_ derived from the atmosphere, or from certain imaginary _Bacteria_ germs,[20] which we are supposed to be unable to distinguish? M. Pasteur may, moreover, be reminded that when he resorts to the supposition of _Bacteria_ possessing “germs” which are indistinguishable, he is again resorting to hypothesis rather than to fact, in order to prove the truth of the particular doctrine of fermentation which he advocates. _Bacteria_ are known to reproduce and multiply only by a process of fission; each of the parts into which they divide being nothing more than a part of the original _Bacterium_, and therefore endowed with similar properties of resisting heat, desiccation, and other agencies. Any resort to invisible germs to account for the multiplication of _Bacteria_, which are known to reproduce freely in other ways, is obviously not permissible, unless such postulation be more or less necessitated by the occurrence of facts otherwise inexplicable. [19] See p. 57.