Inferences.

That boiled ammonic-tartrate solution is a fluid inoculable by living Bacteria, &c., and favourable for their growth and rapid multiplication.

That Bacteria, Vibriones, and their supposed germs are either killed or deprived of all power of multiplication when heated to 140° F. in this fluid. The precisely similar behaviour of the turnipand hay-infusions of series C and series D respectively shows that the Bacteria, Vibriones, and their supposed germs are as inoperative in series Das they are known to be in series C; whilst the behaviour of the hayinfusions shows that they are little amenable to the influence of the drop of the saline fluid when its living units are killed.

Shows that the heat of 131° F. is not sufficient to kill Bacteria, Vibriones, and their supposed germs in organic infusions, and, again, that turnip-infusions are more rapidly influenced by such an inoculating agent than some hay-infusions.*

No experiments could speak more decisively. Those of series B show that Bacteria, Vibriones, and their

These experiments of series C, D, and E were many times repeated with specimens of the same turnip- and hay-infusions, the specific gravity of the former being about 1008 and that of the latter 1005. Different Specimens [of the material to be infused, and] of hay especially, vary so much that it becomes absolutely essential to use portions of the same infusion for the comparative experiments of these different series.

supposed germs are either actually or potentially killed when heated to 140° F. in the neutral saline fluid, which the experiments of series A show to be eminently favourable for their growth and reproduction. Being certain, therefore, that the living units are killed in the drops with which the fluids of series C were inoculated (because they were drops of the same fluid as was employed in series B), we may be equally certain that the turbidity and putrefaction which did ensue in the turnip-solutions of series C were due to the influence of the mere dead constituents of these drops of the turbid saline fluid; whilst, seeing that the behaviour of the fluids of series D was precisely similar to those of series C, we have a perfect right to infer that this series of fluids (D) was as devoid of living units as those of C are known to be-that is, that Bacteria, Vibriones, and their supposed germs are killed by the temperature of 140° F. in organic fluids, just as they are in saline fluids, although, as shown by the experiments of series E, they do not succumb to a heat of 131° F These experiments of series C and D further illustrate the different degrees of amenability of different organic fluids to the same dead ferments; whilst the comparison of the results with the hay-infusions of series C and D with those previously cited (in which the inoculating compound was a drop of an organic

infusion heated to the same temperature of 140° F.) will illustrate the different influence of dissimilar dead ferments upon infusions of the same kind.

The evidence now in our possession shows, therefore, that whilst the temperature at which living ferments cease to be operative varies within very narrow limits (131°-140° F.),* that which destroys the virtues of not-living ferments varies within much wider limits, and depends not only upon the amount of heat employed, but also upon the nature of the putrescible or fermentable liquid to which such ferment is added, in conjunction with the degree of heat and other conditions to which the mixture is subsequently exposed. Here, therefore, we have evidence as to the existence of a most important difference between living and not-living ferments, which has always been either unrecognised or more or less deliberately

* Liebig has proved that a temperature of 140° F. kills Torula, and always suffices to arrest a process of fermentation taking place under their influence in a sugar solution. Torula heated in water to 140° F. also fail to initiate fermentation in a sugar solution. I have also found that an exposure to a temperature of 131° F. for five minutes always suffices to destroy the life of Desmids, Euglenæ, Amœbæ, Monads, Ciliated Infusoria, Rotifers, Nematoids, and other organisms contained in specimens of pond-water. All these lower organisms seem to be destroyed at about the same temperature, as might have been expected from the fundamental relationship which must exist between these several varieties of the one substance-living matter.

+ See "The Beginnings of Life," vol. i., p. 437.

This

ignored by M. Pasteur and his followers.* difference is, moreover, thoroughly in accordance with the broad physico-chemical theory of fermentation which has been so ably expounded by Baron Liebig and others, and the truth of which may now be regarded as definitely established. According to this theory 'living' matter, as a ferment, would take rank merely as a chemical compound having a tolerably definite constitution; and this, we might reasonably infer, would, like other chemical compounds, be endowed with definite properties—and amongst others that of being decomposed or radically altered by exposure to a certain amount of heat. Looked at also from this essentially chemical point of

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* See, for instance, all M. Pasteur's celebrated experiments in which he had recourse to an ensemencement des poussières qui existent en suspension dans l'air," as recorded in chaps. iv. and v. of his memoir in "Ann. de Chimie et de Physique," 1862. M. Pasteur was engaged in an investigation one of the avowed objects of which was to determine whether fermentation could or could not take place without the intervention of living organisms, which M. Pasteur held (in opposition to many other chemists) to be the only true ferments. In his inoculating compound (dust filtered from the atmosphere), there was, as M. Pasteur was fully aware, a large amount of what his scientific opponents considered notliving ferment, whilst possibly there existed a certain number of living ferments. In explaining the results of his experiments, however, M. Pasteur and others thought he was pursuing a logical and scientific method when he attributed these results to the action of the possibly existing element of the inoculating compound, whilst he ignored altogether the other element which was certainly present in comparatively large quantity, and the testing of whose efficacy was the ostensible object of his research.

I

view, it would be only reasonable to expect that the molecular movements of living ferments with a lowered vitality might not be more marked or energetic than those which many not-living organic substances are apt to undergo; and this being the case, we might expect that there would often be a great practical difficulty in ascertaining whether a ferment belonging to the arbitrary and artificial (though, in a sense, justifiable and natural) category of "living" things had or had not been in operation.

It has, moreover, been most unmistakably proved that the limits of vital resistance to heat which Bacteria, Vibriones, and their supposed germs are capable of displaying are essentially the same in the three type fluids which I have employed—that is, in a weak saline fluid, in a neutral organic infusion, and in an acid organic infusion. No evidence exists really tending to show that these organisms or their germs are capable of withstanding the effects of heat better in one of such fluids than in another. We may

therefore safely affirm that M. Pasteur never had any valid evidence in support of his conclusion that the germs of Bacteria and Vibriones can resist heat better in neutral or slightly alkaline solutions than in slightly acid mixtures. The experimental results which led him to arrive at such a conclusion were not logically capable of receiving any such interpretation, whilst