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Fourth Set of Experiments (XXXI.–XXXVII.)

b. Fluid in contact with ordinary Air and its Particles; Flask Sealed after the Fluid had become Cold

No. XXXI. – Healthy Urine remained in the warm bath for twenty-eight days without undergoing the least change.

No. XXXII. – Simple Turnip Infusion remained in the warm bath for twenty-eight days without undergoing any appreciable change.⁵⁹ On breaking the neck of the flask, the fluid was found to be quite odourless. With its neck quite open, the flask was replaced in the water-bath. During the first forty-eight hours it underwent no apparent change, though at the end of seventy-two hours a slight general turbidity was noticeable, and an examination of a drop of the fluid (still odourless), showed a number of minute but very active Bacteria.⁶⁰

c. Fluid in a Bent-Neck Flask, having Eight acute Flexures

No. XXXIII. – Simple Turnip Infusion showed no change after eight days’ immersion in the warm bath. After eleven days, the fluid being still clear, the tube was broken just beyond the second bending from the bulb, and then the flask was re-immersed in the bath. After three days’ exposure, the fluid being still clear, it was boiled in the flask for one minute, when it was noticed that the steam was quite odourless. The flask was then replaced in the water-bath, where it remained for twenty-two days (still with the neck open and broken just beyond its second bending) without showing any change.⁶¹ It was then submitted to examination; the fluid was found to be devoid of all odour, it had a slightly bitter taste, and its re-action was very faintly acid. On microscopical examination no living things were found; there were no Bacteria, no Vibriones, and no Torulæ, only some mere granules, a small amount of amorphous matter, and a few fibres.⁶²

No. XXXIV. – Turnip Infusion Neutralized by Ammonic Carbonate in forty-eight hours showed a slight turbidity, which slowly increased during the next two days. In two days more the turbidity was very great, and there was also a considerable amount of sediment. The fluid was then examined microscopically, and found to contain myriads of large but very languid Bacteria.

e. Fluid (in vacuo) in a Flask which had been Sealed during Ebullition

No. XXXV. – Healthy Urine underwent no apparent change for the first twelve days, then (the bulk of the fluid still remaining clear and bright) small greyish white flocculi began to collect at the bottom of the flask, which very slowly increased in quantity during the succeeding twelve days. At the expiration of this time the flocculi were pretty numerous, though the fluid was otherwise bright. The vacuum was ascertained to be still good, and on breaking the flask, the fluid was found to have a slightly acid re-action, though no appreciable odour. When examined microscopically, the flocculi were seen to be made up for the most part of mere granular aggregations (simple, and not in the form of Bacteria). Small Torula cells, however, existed in some quantity; also a few necklace-like chains, and a comparatively small number of Bacteria, some of which were tolerably active.

No. XXXVI. – Simple Turnip Infusion after twenty-four hours showed no sign of change, though in thirty-six hours it was slightly turbid. On the fourth day the turbidity was well-marked and general, though there were no flake-like aggregations. When examined microscopically, the fluid was found to contain multitudes of Bacteria.

No. XXXVII. – Turnip Infusion, ⁶³ Neutralized by Ammonic Carbonate in twenty-four hours was decidedly turbid. In thirty-six hours the turbidity was more marked, and there was a slight sediment. By the end of forty-eight hours both turbidity and sediment had notably increased. On the fourth day, there was a moderately clear fluid, containing an abundance of curdy or flake-like masses. When the flask was opened, these were found to be made up principally by the aggregation of myriads of Bacteria.

Fifth Set of Experiments (XXXVIII.–XLVII.)

Fluids not boiled, but half-filling hermetically Sealed Flasks, containing Ordinary Air

No. XXXVIII. – Turnip Infusion in ten hours showed a slight amount of turbidity. After forty-eight hours this was very well-marked: there was a thick pellicle on the surface, and, in addition, a small amount of deposit. On examination, the fluid and the pellicle were found to contain an abundance of Bacteria, Vibriones and Leptothrix filaments.

No. XXXIX. – Turnip Infusion + 1/20 of Carbolic Acid after eight days showed no appreciable alteration in appearance,⁶⁴ no trace of pellicle or deposit. When examined microscopically, however, the fluid was found to contain some very minute Bacteria, though they were by no means abundant.

No. XL. – Hay Infusion had become quite turbid in twenty-four hours, and several shades lighter in colour. After forty-eight hours the colour of the infusion was still lighter; there was more turbidity, and some sediment. On microscopical examination, the fluid was found to contain an abundance of Bacteria, Vibriones and short Leptothrix filaments.

No. XLI. – Hay Infusion + 1/20 of Carbolic Acid showed no apparent change⁶⁵ after forty-eight hours, and when examined microscopically it revealed no trace of Bacteria, or other organisms. The neck of the flask was then again closed. On the twelfth day the fluid had still undergone no change in appearance, and when examined microscopically, it still showed no trace of organisms, though the fluid was – as it had been at the time of the first examination – full of minute, undissolved particles of carbolic acid.

Fluids boiled for five minutes, and half-filling hermetically Sealed Flasks containing Ordinary Air

No. XLII. – Hay Infusion, after forty-eight hours, showed no change, and continued to remain quite clear and free from deposit until the twelfth day, when it was examined microscopically. No organisms of any kind could be detected.

No. XLIII. – Hay Infusion + 1/20 part of Carbolic Acid showed no apparent change⁶⁶ for the first five days, though, on the sixth day, a slight deposit was noticed at the bottom of the flask. The deposit had increased, and was well-marked by the twelfth day, when, on microscopical examination, there were found amongst the granular flakes of the deposit, Torulæ of several varieties of size and shape. Many were spherical, others ovoid, or having an elongated oat-like shape: some were of the ordinary colour, and others were brownish in tint. The variety was most striking. No Bacteria were seen, though there were multitudes of active particles which seemed to differ from the minute spherules of undissolved carbolic acid.

Fluids (in vacuo) – boiled for five minutes, and Flasks Sealed during Ebullition

No. XLIV. – Turnip Infusion, in seventy-two hours, showed a slight turbidity, which gradually increased. On the eighth day there was a considerable quantity of flake-like sediment, and some amount of general turbidity. On the thirteenth day the vacuum was found to be still partly preserved. When the flask was opened the fluid was perceived to have a fœtid odour, and an acid re-action; and, on microscopical examination, multitudes of Bacteria and Vibriones were seen. In the flake-like aggregations also (made up almost wholly of these organisms) there were a number of large thick-walled spores; some already formed, and others in process of formation by coalescence.

No. XLV. – Turnip Infusion + 1/20 part of Carbolic Acid showed no increase of turbidity⁶⁷ for the thirteen days during which it was kept under observation. Before the flask was opened it was ascertained that the vacuum was well preserved. The odour of the fluid was unaltered, and on microscopical examination no Bacteria, or other living things, were found.⁶⁸

No. XLVI. – Hay Infusion, after forty-eight hours, showed no change, though, in seventy-two hours, there was perceptible a very small amount of a dirty greyish deposit. By the fifth day the deposit had slightly increased, and on the seventh day there was a trace of turbidity in the fluid. It did not undergo much further change, so that, on the twelfth day, the flask was opened. The vacuum was found to have been very slightly impaired; the odour of the fluid was almost natural, and its re-action was slightly acid. On microscopical examination of the deposit, Bacteria, Vibriones, short Leptothrix filaments, and Torulæ, were found, though not in very great abundance.

No. XLVII. – Hay Infusion + 1/20 part of Carbolic Acid showed no apparent change for the first four days. On the fifth day there was a small quantity of powder-like sediment, and one dirty greyish-coloured flake. On the seventh day there were more small flakes at the bottom, and a slight general turbidity of the fluid. On the twelfth day, the turbidity and deposit having increased, the flask was opened – after it had been first ascertained that the vacuum had only been slightly impaired. The re-action of the fluid was still strongly acid. On microscopical examination of some of the deposit, there was found, amongst granular flakes and aggregations, a large number of Torulæ cells, of most various shapes and sizes; also in the midst of the granule heaps many large, rounded or ovoidal, densely granular nucleated bodies, whose average size was 1/1500″ in diameter, though there were many of them much larger, and others even less than half this size. Intertwined amongst the granular matter also were a large number of algoid-looking filaments, 1/20000 in diameter, containing segmented protoplasmic contents. There were also in the fluid itself a number of medium-size, unsegmented Bacteria, whose movements were somewhat languid.⁶⁹

Sixth Set of Experiments (XLVIII.–LXV.)

Ammoniacal Solutions, unboiled, and exposed to Ordinary Air in a Corked Bottle. ⁷⁰ (Temp. 60°–65° F.)

No. XLVIII. – Ammonic Acetate Solution.– On the tenth day the fluid was still quite clear, and free from sediment.

No. XLIX. – Ammonic Oxalate Solution.– On the tenth day there was no distinct opalescence of the fluid, but a well-marked whitish flocculent deposit. On microscopical examination no Bacteria were found in the fluid, and the deposit was made up by an aggregation of blackish and colourless granules, mixed with a few crystals and a very few Torula cells – all being held together by a sort of mucoid matrix. In the midst of this matter were found two or three very small, much branched, mycelial tufts of a fungus-growth.

No. L. – Ammonic Carbonate Solution.– On the tenth day the fluid showed a very faint opalescence, with a small amount of deposit, and a partial non-coherent scum on the surface, which, on microscopical examination, was found to be composed partly of amorphous granules, and partly of minute Bacteria, mixed with small necklace-like organisms. The fluid itself contained, in suspension, a few small and sluggish Bacteria, with a minute Torula cell here and there.

No. LI. – Ammonic Tartrate Solution after twenty-four hours showed the faintest opalescence of the fluid; in forty-eight hours there was a bluish-white turbidity, and in seventy-two hours the turbidity was well marked. When examined microscopically the fluid was found to contain multitudes of very active Bacteria. On the thirteenth day the turbidity was not so well marked, though there was a very thin pellicle on the surface, and also the dirty-looking crumpled remains of another pellicle at the bottom, which, on examination, was found to be composed of an aggregation of Bacteria. The pellicle on the surface was very thin, and composed only of a single layer of Bacteria. In the fluid itself many Bacteria were seen, of medium size, and mostly sluggish in movement, though a few of them exhibited very active rotatory movements. No Vibriones, Leptothrix, or Torulæ, were found.

No. LII. – Ammonic Tartrate and Sodic Phosphate Solution after twenty-four hours showed the faintest opalescence; in forty-eight hours there was a bluish-white turbidity, which, in seventy-two hours, had become more marked. When examined microscopically multitudes of Bacteria were found whose movements were very sluggish. On the thirteenth day there was a well-marked whitish turbidity, due to Bacteria and Vibriones, a slight amount of deposit, and a firm pellicle which was found to be composed, almost wholly, of long unjointed Vibriones and unsegmented Leptothrix filaments, all of which, when separate, exhibited the most distinct eel-like movements, accompanied by an actual progression from place to place.

Ammoniacal Solutions, unboiled, and exposed to Air in a Corked Bottle, after Inoculation with a Drop of Fluid containing living Bacteria and Torulæ. (Temp. 60°–65° F.)

No. LIII. – Ammonic Acetate Solution after twenty-four hours was faintly opalescent, and in forty-eight hours showed a very slight bluish tint. In seventy-two hours it was in the same state, and, on microscopical examination, the fluid showed no distinct Bacteria or other living things, though there were a number of very minute particles distributed, singly or in small groups, throughout the fluid. On the thirteenth day there was no change in appearance, except that the sediment had somewhat increased in amount. Still, no Bacteria could be found in the fluid or the sediment, – only the above-mentioned particles, and a few somewhat larger, which resembled very minute Torulæ. Amongst the sediment, however, there were two or three very small mycelial tufts of a developing fungus.

No. LIV. – Ammonic Oxalate Solution.– On the eighth day the fluid showed a very faint opalescence, though there was a well-marked, greyish, flocculent deposit, which was found to be composed of an aggregation of colourless and blackish granules, of a multitude of minute crystalline particles (mostly diamond-shaped), and some rounded or ovoidal, thick-walled, spore-like bodies; amongst which, and enveloped in part by them, were several mycelial tufts of a fungus. A number of minute Bacteria were found distributed throughout the fluid, and also a quantity of minute star-like bodies (crystalline), about 1/12000 in diameter.

No. LV. – Ammonic Carbonate Solution.– On the eighth day the fluid showed a very faint opalescence, and a slight deposit, which was found to be composed principally of amorphous granules. Distributed through the fluid were some small and sluggish Bacteria, though no other organisms were seen.

No. LVI. – Ammonic Tartrate Solution.– After twenty-four hours the fluid showed the faintest opalescence, and in forty-eight hours there was a slight bluish-white turbidity. In seventy-two hours the turbidity was well marked, and there was a very thin pellicle on the surface. When examined microscopically the fluid was found to contain multitudes of very active Bacteria, and the pellicle was also composed of an aggregation of Bacteria. On the thirteenth day the opacity had somewhat increased; there was also a well-marked pellicle, and an obvious deposit. The pellicle was found to be composed of Bacteria, and in the fluid there were multitudes of medium-size Bacteria and Vibriones, with here and there a small Torula cell.⁷¹

Ammoniacal Solutions (in vacuo) in Flasks which were hermetically Sealed during Ebullition of their Fluids at a Temperature of 90° F. ⁷² (Subsequently exposed in water-bath to a Temperature of 75°–85° F.)

No. LVII. – Ammonic Tartrate Solution after sixty hours showed a slight sediment, with bluish flakes attached to sides of flask. In eighty-four hours there was a general bluish opalescence, and on microscopical examination the fluid was found to contain multitudes of Bacteria.

No. LVIII. – Ammonic Tartrate and Sodic Phosphate Solution.– After sixty hours there was a slight general bluish opalescence. In eighty-four hours the general opalescence was not more marked, but there were many flake-like aggregations in the fluid, which on microscopical examination were found to be aggregations of Bacteria.

Ammoniacal Solutions boiled (at 212° F.), and exposed to Air in Flasks whose Open Necks were only loosely covered with Paper Caps: subsequent Inoculation. (Temp. 75°–85° F.)

No. LIX. – Ammonic Tartrate Solution.– The fluid remained quite clear, and free from all trace of turbidity up to the ninth day, when it was inoculated with some living Bacteria. In fifty hours after the inoculation there was a very faint opalescence of the fluid, which, in another 24 hours, had become much more marked. On microscopical examination it was found to contain multitudes of Bacteria.

No. LX. – Ammonic Tartrate and Sodic Phosphate Solution.– After four days the fluid was still quite clear. In seven days no trace of general turbidity, though there was a minute dirty-grey aggregation about 1/14″ in diameter at the bottom of the flask. On the sixteenth day the grey aggregation had very slightly increased in size, though the fluid above was still perfectly clear. The grey mass was removed by a small pipette, and, on microscopical examination, it was found to be composed of an aggregation of minute extraneous fibres, mixed with blackish particles and amorphous granular matter, in which were growing many Torula-cells in all stages of development, and also a minute mycelium composed of branched Leptothrix-like fibres.⁷³ The clear fluid was then inoculated with some living Bacteria, and the bulb of the flask was replaced in the warm bath. After fifty hours the solution showed a bluish turbidity, which, in thirty-six hours more, had increased to a well-marked whitish opacity, and when examined, the fluid was found to be swarming with active Bacteria.

Solutions of Ammonic Tartrate and Sodic Phosphate were heated, in their respective Flasks, for Fifteen Minutes to the Temperatures mentioned below. The Necks of the Flasks were afterwards loosely covered with Paper Caps, whilst the Bulbs were immersed in a Water-Bath kept at a Temperature of 75°–85° F

No. LXI. —

Solution heated to

149° F.

No. LXII.

" " "

158° F.

No. LXIII.

" " "

158° F.

No. LXIV.

" " "

167° F.

No. LXV.

" " "

167° F.

All these solutions remained quite clear and free from any trace of general turbidity for ten days. Each fluid was then inoculated with some living Bacteria, and in the space of thirty-six to seventy-two hours, all had become more or less obviously turbid, and on microscopical examination this turbidity was found in each case to be almost wholly due to the presence of multitudes of Bacteria.

Interpretation of the Experiments: Conclusions as to the Cause of Fermentation, and as to the Occurrence of Archebiosis

These experiments seem to show quite conclusively that M. Pasteur’s explanations are altogether inadequate to account for the occasional preservation of boiled fluids in bent-neck flasks. They show that the preservation, far from being universal, is only occasional, and that preservation or non-preservation of different fluids is almost wholly dependent upon their nature. They lend no countenance, moreover, to his particular theory, that fermentation cannot be initiated without the agency of living ferments, – they are, on the contrary, wholly opposed to this restriction.

The plug of cotton-wool, or the narrow and bent tube may, it is true, protect the boiled fluid from subsequent contact with living “germs”; but that the fluids do not undergo change on account of such deprivation cannot be safely affirmed, when the same means would also filter from the fluid some of the multitudinous particles of organic matter (dead), which the air undoubtedly contains, and which may act as ferments. It must be remembered that the main object of M. Pasteur’s investigation was to determine whether fermentation took place under the agency of mere dead nitrogenous matter, as Liebig and others affirm; or whether it is only initiated by living organisms, as he himself supposes. Obviously, therefore, the same filtration which purified the air from any living organisms would filter from it its nitrogenous particles, which are the other possible ferments: so that no conclusion could be drawn from such experiments, more favourable to the one than to the other of these hypotheses. All that could have been safely affirmed was, that by boiling the fluid, and then protecting it from subsequent contact with everything that could act as a ferment, fermentation would not take place.

Even this however, – as the preceding experiments fully show – cannot be truly affirmed to be a general rule. Some infusions do undergo change, notwithstanding this treatment and deprivation, whilst others do not: that is to say, some still preserve a first degree of fermentability even after boiling, whilst others are reduced by this process to the second degree of fermentability. These latter are unable to initiate changes by virtue of their own inherent instability; molecular re-arrangements require to be set on foot in them by contact with some more unstable substance, which is itself undergoing change.

That such is the correct explanation of the reason why some fluids do not ferment in bent-neck flasks, seems obvious from the discordant results obtained in many other experiments, after the free admission of uncalcined air to the fluids which had been boiled. The fluids were deprived of their virtues in some cases by the heat to which they had been subjected, so that whether they underwent change or not, may have depended upon the accidental presence or absence, in the air which was subsequently admitted to the fluid, of some unheated organic fragments, capable of initiating fermentative changes. If germs were as omnipresent as they have been represented to be, such fluids ought always to have undergone fermentation.

Whilst I have found that any given fluid, whose strength is about equal on different occasions, acts in a definite manner when the flask is hermetically sealed after expulsion of all its air and during the continuance of ebullition; and, whilst a like definite result can generally be obtained, when calcined air is admitted to the boiled fluid before the vessel is hermetically sealed; it is found, on the other hand, that the result is in no way predicable when uncalcined air is admitted. Sometimes fermentation takes place, and sometimes in other flasks – sealed at the same time, and subsequently placed under the same conditions – no change whatever occurs. My own experience in this respect accords perfectly with that of M. Pasteur.⁷⁴ He, however, at once came to the conclusion that the only inference from such facts was that “germs” are not so universally distributed as they had been supposed to be by Bonnet and Spallanzani.⁷⁵ The unprejudiced inquirer, however, will perceive that M. Pasteur was entitled to come to no such conclusion concerning germs which was not equally applicable to minute fragments or débris of organic matter floating in the air. And, similarly, the evidence which he adduces with regard to the diminution in the number of the fertile flasks when they were filled with some of the still air of the caves of the observatory, or else with some from the peaks of the Jura,⁷⁶ far away from the haunts of men, had no bearing upon the distribution of germs which was not equally applicable to that of dead organic particles. Such evidence, therefore, was valueless for settling between the rival doctrines of fermentation – it could not possibly help us to decide whether living or dead ferments were necessary. Dead organic particles would sink in still air in the same manner as living organisms;⁷⁷ and similarly, dead organic particles, have been shown to be less and less numerous in the atmosphere in proportion to the elevation obtained.⁷⁸ In these latter experiments M. Pasteur made use of yeast-water (alone or sweetened), and of urine – all three of them fluids, which, after having been boiled, are apt to possess only the second degree of fermentability. Shortly afterwards, M. Pouchet, in concert with MM. Joly and Musset,⁷⁹ repeated these experiments, with the sole difference that they employed strong infusions of hay – which experiment has shown almost invariably to possess the first degree of fermentability. And seeing that all their flasks, after a time, yielded organisms from whatever mountain elevation the air had been taken – the combined evidence tends strongly against the view of M. Pasteur. Since the germs in the fluids and in the flasks, in each set of experiments, had been previously destroyed by ebullition, and since in each set, also, air of the same character had been admitted to the boiled fluids, the different results seemed to show that fermentation or non-fermentation, in such cases, depends wholly upon the quality of the fluids employed.

Other evidence which is so much vaunted by M. Pasteur and his supporters, as to the possibility of inducing fertility in previously sterile flasks, by the addition of a portion of asbestos containing the solid particles filtered from the atmosphere,⁸⁰ is also equally valueless for confirming the proposition that fermentation is only capable of being initiated by living ferments. The same asbestos which may contain living spores or organisms (“germs”), does undoubtedly contain many decomposable particles and fragments of organic matter.⁸¹ The previously barren solution may therefore be rendered fertile by the mere addition of those portions of unstable organic matter, whose molecular mobility has not been impaired by the agency of heat, and which are therefore capable of initiating fermentations. This view is strengthened, as M. Pouchet has pointed out, by the fact that in these cases, instead of meeting some of the various kinds of organisms which are supposed to have representatives in the air, and whose spores or ova may be supposed to have been sown, it is often merely Bacteria which are encountered, – differing in no respect from those that may present themselves in a somewhat similar infusion, which has undergone change in a closed flask without any such hypothetical sowing of living spores or germs. It is more especially important to bear in mind this consideration, when portions of organic matter can always be easily demonstrated amongst such atmospheric dust; whilst living Bacteria, or other organisms, such as are first produced as a result of the supposed sowing of spores, either cannot be demonstrated, or would seem, from other evidence, to be at least very sparingly distributed.⁸²

The fact revealed by M. Pasteur, that some fluids remain unchanged for an indefinite period, after having been boiled in flasks, with long and bent necks, is easily explicable in accordance with the physical theory of fermentation, and now that it has been thoroughly proved that other fluids – submitted to precisely similar conditions – do nevertheless undergo fermentation, this fresh fact is just as completely adverse to the explanations and views of M. Pasteur, as it is thoroughly harmonious with the doctrines of Baron Liebig. The fluids which are capable of being preserved – generally not presenting a high degree of fermentability – do not undergo change, at ordinary atmospheric pressure, after having been boiled, unless they are brought into contact either with some pre-existing living things or with some unaltered organic particles from the atmosphere. Neither of these, however, can gain access to the fluid, in such a vessel; because all the air which enters, after the first inrush into the still almost boiling fluid, has to pass, more or less slowly, through the numerous flexures of the narrow neck of the flask and the two or three strata of fluid which always remain therein.

Some of the fluids which do not undergo change in these bent-neck vessels are, however, by no means notable for possessing a low degree of fermentability. This is the case, for instance, with infusions of turnip, which, under other conditions, have been found to be most prone to undergo fermentation. And, I have found in several cases in which such an infusion had been exposed in a bent-neck vessel, and had remained unchanged for twelve or fourteen days (even though subjected to a temperature of 85°–95° F.), that if the neck of the flask were then broken shortly above the bulb, the solution would still continue without alteration for a week, ten days, a fortnight, or even more – although freely exposed to the air, and therefore to the access of any living germs which might be floating about in the atmosphere.⁸³

The views hitherto expressed with reference to the causes of fermentation and putrefaction, and to the interpretations which M. Pasteur’s experiments are capable of receiving, seem to derive all the additional support that can be needed, from the results of my own experiments with boiled fluids, in sealed flasks, from which all air had been expelled.

Some of the same fluid being taken and divided into three parts, each portion is placed in a separate flask, in which it is boiled for a period of ten minutes. One of the flasks (A) is provided with a long and bent neck, so that the air which re-enters is deprived of its germs and organic particles; another (B) has only a short neck, and to this, the access of germs and organic particles is freely permitted till the fluid has become cool, and then the neck of the flask is hermetically sealed; whilst the last (C) is sealed during ebullition, after all air has been expelled. Now, if Pasteur’s theory of fermentation, and the prevalent notions concerning the universal distribution of “germs” throughout the atmosphere were true, it might be expected that the fluid in B would always rapidly change; that that in A would always remain pure; and that the fluid in C would, similarly, undergo no alteration. The facts, however, are quite the reverse: if a strong turnip infusion be employed, the fluid in A will almost always remain unchanged; that in B will sometimes rapidly change, and at other times will remain quite pure; whilst that in C will almost invariably become turbid in from two to six days. But, even if it were not the case that some fluids, different from those used by M. Pasteur, will almost invariably undergo change in bent-neck vessels, M. Pasteur’s explanation of the cause of the preservation would have been altogether upset by the fact that some of the very fluids which remain pure in the bent-neck apparatus will become fœtid if shut up in vacuo. It is, therefore, of course useless to talk of a particular boiled fluid having been saved from putrefaction on the ground that the living atmospheric germs (whose presence is supposed to be necessary for the initiation of such a process) have been altogether filtered from the re-entering air, when some of the same fluid will putrefy, if placed under different conditions by which it is freed both from the influence of the atmosphere and from its germs —i. e., when, instead of filtering the re-entering air, no air is permitted to enter. Germs and atmospheric particles being equally got rid of in both sets of cases, the great difference between them is that the weight of the atmosphere is also got rid of in my experiments – the fluids being contained in vacuo. Now it has been ascertained by Mr. Sorby, that pressure undoubtedly influences “chemical changes taking place slowly, and therefore, probably due to weak or nearly counterbalanced affinities;” and he also states, in the Bakerian Lecture for 1863,⁸⁴ that “a considerable number of facts have been described, showing that pressure will more or less influence such chemical actions as are accompanied by an evolution of gas, so that it may cause a compound to be permanent, which otherwise would be decomposed.” If increase of pressure retards, a diminution of pressure will facilitate such chemical changes, so that one can only explain the results which I have obtained, on the ground that many boiled fluids, which will not undergo change when protected from the influence of atmospheric particles (living or not living) at the same time that they are subjected to ordinary or increased pressure, will, on the contrary, pass through such changes when pressure is removed, and the fluids are preserved in vacuo. It is not pretended that this is a rule applicable to all organic fluids – far from it. Diminution of pressure does seem, however, to be a very potential cause of change in some fluids. The extent to which changes of a fermentative character can progress in the absence of atmospheric oxygen, is also evidently subject to much variation, in accordance with the nature of the dissolved fermentable substances.