Such experiments would seem to be most important and crucial in their nature. They may be considered to settle the question as to the vital resistance of these particular Bacteria, whilst other evidence points conclusively in the direction that all Bacteria, whencesoever they have been derived, possess essentially similar vital endowments[42]. Seeing also that the solutions have been inoculated with a drop of a fluid in which Bacteria, Vibriones, and Torulæ are multiplying rapidly, we must suppose that they are multiplying in their accustomed manner, as much by the known method of fission, as by any unknown and assumed method of reproduction. In such a fluid, at all events, there would be all the kinds of reproductive elements common to Bacteria, whether visible or invisible, and these would have been alike subjected to the influence of the same temperature. These experiments seem to show, therefore, that even if Bacteria do multiply by means of invisible gemmules as well as by the known process of fission, such invisible particles possess no higher power of resisting the destructive influence of heat than the parent Bacteria themselves possess. This result is, moreover, as I venture to think, in accordance with what might have been anticipated à priori. Bacteria seem to be composed of homogeneous living matter, and any gemmule, however minute, could only be a portion of such living matter, endowed with similar properties.
Extent to which boiled Fermentable Fluids may be preserved in Vessels with Bent Necks, or in those whose Necks are guarded by a Plug of Cotton-Wool.
Having thus satisfied ourselves as to the truth of the conclusion that Bacteria are killed when the fluid containing them is boiled (at 212° F.), we are in a position to proceed with the inquiry as to the evidence which exists in respect to the statements made by M. Pasteur, Professor Huxley, and others, that fermentable fluids which have been boiled, will not undergo fermentation, either in vessels whose necks have been many times bent, or in those into whose necks a plug of cotton-wool has been inserted during the ebullition of their contained fluid. Organisms are not found in such cases, they say, because the “germs” from which the low organisms of infusions are usually produced, are arrested either in the flexures of the tube or in the cotton-wool. As I have before stated, however, it is obvious that if this explanation be the correct one, the preservation should be equally well marked in all cases—quite irrespectively of the amount of albumenoid or other nitrogenous material which may be contained in the fluid. Any exceptions to the rule should at once suggest doubts as to the validity of the explanation.
It was shown[43] in 1865 by M. Victor Meunier that some fluids were preserved after having been boiled in a vessel of this kind, whilst others, submitted to the same treatment, speedily became turbid from the presence of Bacteria and other organisms.[44] By these experiments he ascertained that strong infusions did frequently change, whilst weak ones might be preserved; and that even a strong infusion might be prevented from undergoing change if the period of ebullition were sufficiently prolonged.
The fluids most frequently employed by M. Pasteur were yeast-water, the same sweetened by sugar, urine, infusion of beetroot, and infusion of pear.
Taking urine as a fair example of such a fluid, I have found that the statements of M. Pasteur and of Professor Lister are perfectly correct. This fluid may generally remain for an indefinite period in such vessels[45] without becoming turbid, or undergoing any apparent change. The same is generally found to be the case with an infusion of turnip, and occasionally an infusion of hay may be similarly prevented from undergoing fermentation. On the other hand, if the turnip-solution be neutralized by the addition of a little ammonic carbonate, or liquor potassæ; or, better still, if even half a grain of new cheese be added to the infusion before it is boiled, then I have found that the fluid speedily becomes turbid, owing to the appearance of multitudes of Bacteria. In an infusion to which a fragment of cheese had been added, I have seen a pellicle form in three days, which, on microscopical examination, proved to be composed of an aggregation of Bacteria, Vibriones, and Leptothrix filaments. A mixture of albuminous urine and turnip-infusion has also rapidly become turbid in a vessel of this kind owing to the appearance of multitudes of Bacteria, and so has a mixture containing one-third of healthy urine with two-thirds of infusion of turnip.
Other infusions have been boiled for ten minutes in a vessel with a horizontal neck two feet long, into which, during ebullition, a good plug of cotton-wool had been carefully pushed down for a depth of twelve or fourteen inches, and cautiously increased in quantity during the continuance of the ebullition; whilst immediately after the withdrawal of the heat, the plug was pressed closer, and all the outer unoccupied portion of the tube was rapidly filled up in the same manner.
Preserved in such a vessel, a specimen of urine remained unchanged; a hay-infusion also underwent no apparent alteration; whilst a very strong infusion of turnip became turbid in five days, and ultimately showed a large quantity of deposit.[46]
Thus the rules laid down by Pasteur and others are not universal, and therefore, as I have previously pointed out, the explanation which he adduced of the preservation of those particular fluids which remained unchanged is at once rendered doubtful. More especially is there room for doubt on this subject when, as I have found, the result of the experiment can be, within certain limits, predicated beforehand, according to the nature of the fluid employed. If all organisms proceed from pre-existing germs, and these can be filtered from the air by a certain mechanical contrivance, then, if it be alleged that it is on account of such filtration that certain boiled fluids do not change, all fluids placed under these conditions ought, on this theory, to be similarly preserved. Exceptional cases cannot be accounted for on this hypothesis. To others, however, who say that organisms are capable of arising de novo, and that fermentation can be initiated without the agency of living things, the above facts appear quite natural. The more complex the nitrogenous or protein materials contained in a solution, the more is it fitted to undergo fermentative changes, which may be accompanied by the de novo origination of living things. Therefore the above results are just as compatible with the notions of M. Liebig and his school, as they are antagonistic to those of M. Pasteur. Certain fluids, it is found, do not undergo change; whilst other fluids, of a more complex description, will ferment under the influence of similar conditions. Prolonged ebullition also, by breaking up some of the more unstable compounds of a solution (those which most easily initiate these changes) will retard or prevent its fermentation.
The complete untenability of M. Pasteur’s explanations are, however, best revealed by having recourse to a series of comparative experiments, in which portions of the same fluid are boiled for an equal length of time in vessels of different kinds, and are then subsequently submitted, in a water-bath, to the influence of the same temperature.