Seeing however, that we are able, with the aid of the microscope alone, to demonstrate that Bacteria and Torulæ can develop in situations where no visible germs had previously existed, it is useless, as I have said before—so far as the question of their mode of origin is concerned—to search the atmosphere to ascertain what visible germs it may contain. If some Bacteria and Torulæ arise from germs at all, it must be from germs which are invisible to us. The finding of visible germs in the atmosphere can, therefore, only have an indirect bearing upon the solution of the problem. Since it can be shown that some visible spores and ova exist in the atmosphere, this affords a certain amount of warrant for the supposition that invisible, living, reproductive particles may also exist—more especially if the existence of an amount of organic matter, which is ordinarily invisible, can be revealed in the air, by the agency of the electric beam, or by any other means.
Nothing can be more illegitimate, however, in the way of inference, than the assumption at once indulged in by Prof. Tyndall and others (who might have been expected, by their previous scientific work, to have learned more caution) that this impalpable organic dust was largely composed of impalpable germs. Yet, without a shadow of proof, without even an attempt to prove it, the air was for a time represented to be a mere stirabout, thick with invisible germs. The briefest reflection, however, upon the probabilities of the case, should have sufficed to suggest a totally different interpretation. The surface of the earth is clothed with living things of all kinds, animal and vegetal, which are not only continually throwing off organic particles and fragments during their life, but are constantly undergoing processes of decay and molecular disintegration after their death. The actual reproductive elements of these living things are extremely small in bulk, when compared with the other parts which are not reproductive, and although Bacteria and Torulæ do exist abundantly, and do materially help to bring about some of the decay in question, yet their bulk, also, is extremely small in comparison with the amount of organic matter itself that is continually undergoing disintegration of a dry kind, in which Bacteria and Torulæ take no part. When, moreover, it is considered that in the neighbourhood of populous cities (the air of which alone exhibits this very large quantity of impalpable, mixed with palpable, organic dust), there is constantly going on a wear and tear of the textile fabrics and of the organic products of various kinds which are daily subservient to the wants of man; and that the chimneys of manufactories and dwelling-houses are also continually emitting clouds of smoke thick with imperfectly consumed organic particles, some idea may be gained of the manifold sources whence the organic particles and fragments found in the atmosphere may emanate, and also as to what proportion of them is likely to be composed of living or dead reproductive elements, or “germs.”
Thus, then, so far as the two rival doctrines of fermentation are concerned, the investigation of the nature of the solid particles contained in the atmosphere has revealed facts which are thoroughly in harmony with all the requirements of Liebig’s physical theory, though it has almost utterly failed to give anything like a scientific basis to the vital theory of Pasteur. So far from being able to show that living Bacteria (which are the first and oftentimes the only organisms concerned in many processes of fermentation and putrefaction) are universally diffused through the air, Pasteur admits that these cannot be detected, and that their “germs” are not recognizable.
If, therefore, M. Pasteur still maintains the truth of his theory, it should be distinctly understood that it rests originally, not upon established facts, but upon a mere hypothesis—the hypothesis that the air teems with multitudes of invisible Bacteria germs. He is driven to such a doctrine, not only by his own confessions concerning Bacteria, but also by the microscopical evidence to which I have referred.
So that in explaining the results of any experiments made with the view of throwing light upon the cause of fermentation or putrefaction, it is especially necessary to bear in mind two considerations:—
I. That dust filtered from the atmosphere cannot be proved to include living Bacteria; though it is known to contain a multitude of organic particles which may be capable in the presence of water, in accordance with Liebig’s hypothesis, of acting as ferments.
II. It must also be recollected that, in the opinion of many, Life represents a higher function which is displayed by certain kinds of organic matter; and that this higher function may be deteriorated or rendered non-existent by an amount of heat which might not be adequate to decompose the organic matter itself.
It is all the more necessary to call attention to these two considerations, because M. Pasteur invariably speaks as though it had been established that the air contains multitudes of living Bacteria, when, really, he had only proved that the air contains a number of corpuscles resembling spores of fungi, &c. And, as I have already intimated, the existence of spores of fungi in the atmosphere, however well established, is of little or no importance as an explanation of the cause of a very large number of fermentations. Their presence is even of still less importance, owing to the fact of the co-existence with these fungus-spores, of multitudes of organic fragments, which—in accordance with the views of Liebig, Gerhardt, and other chemists—are capable of acting as ferments. To this latter consideration M. Pasteur never even alludes when he speaks (loc. cit. p. 40) of his “ensemencements,” and of other experiments which are equally, or even more, capable of being interpreted in accordance with Liebig’s views than with his own.
Bearing these considerations in mind, we shall be in a better position to enquire into the real interpretation that may be given to many of M. Pasteur’s results, and into the question as to how far the facts which he records are favourable to his own, or to the adverse doctrine concerning the causes of fermentation.
In the memoir so often alluded to on “The Organized Corpuscles which exist in the Atmosphere,” M. Pasteur adduced various kinds of evidence, tending, as he thought, to show that the first Bacteria which make their appearance in putrefying or fermenting solutions, have been derived from living Bacteria or their “germs,” which pre-existed in the atmosphere.