The modes of origin of lowest organisms

2. Heterogenetic Mode of Origin of Bacteria and of Torulæ

It has been long known that Bacteria and Torulæ are frequently to be found within vegetable cells, taken even from the central parts of plants, whenever these are in a sickly condition or are actually dying. They are apt to exist also within epithelial cells taken from the inside of the mouth; and the frequency and abundance with which such organisms are met with in these cells, is almost in direct proportion to the malnutrition and lack of vital power in the individual who is the subject of observation. Then, again, in persons who have died of adynamic diseases, in the course of twenty-four or thirty-six hours (during warm weather) Bacteria may be found in abundance within the blood-vessels of the brain and of other parts, although no such Bacteria were recognizable in the blood of the individual during life.

In these cases we must, in order to account for the presence of the Bacteria and Torulæ, either suppose that such organisms, in an embryonic state, are almost universally disseminated throughout the various textures of higher organisms, both animal and vegetal (though they are only able to develop and manifest themselves when the higher organisms, or the parts of them in which the Bacteria or Torulæ are met with, are on the eve of death), or else we must imagine that when the vital activity of any organism, whether simple or complex, is on the wane, its constituent particles (being still portions of living matter) are capable of individualizing themselves, and of growing into the low organisms in question. Just as the life of one of the cells of a higher organism may continue for some time after the death of the organism itself, so, in accordance with this latter view, may one of the particles of such a cell be supposed to continue to live after even cell-life is impossible.

Now, to many persons, the latter seems to be a much simpler hypothesis than the former, and one, moreover, which is more in accordance with known facts. People’s views, however, on this subject are likely to be much influenced by their notions as to the possibility of Bacteria arising by a process of Archebiosis. Although some may be inclined to accept the doctrine of Heterogenesis, the same persons, being “vitalists,” may not readily believe in the doctrine of Archebiosis, because this implies the vivification of dead matter – the conversion of not-living elements into a living combination. Those, however, who do believe in Archebiosis will – if the necessary evidence be forthcoming – all the more readily yield their assent to the doctrine of Heterogenesis, because it is a much less novel thing to have to believe in the mere transformation of living matter, than in the possibility of its origin de novo.

Evidence of a tolerably satisfactory nature, however, is forthcoming, which may speak independently in favour of the doctrine of Heterogenesis.

It has been affirmed by Crivelli and Maggi[6 - Rendiconti del R. Istit. Lombardo, Ser. II. Vol. 1, p. 11.] that they have actually seen the particles within granular epithelial cells (taken from the back of the tongue of a patient suffering from diabetes) grow and elongate, so as to give rise to Bacteria, or fuse in longitudinal series, so as to form a Vibrio.[7 - However novel such a mode of origin of independent Bacteria and Vibriones may appear to some, it will seem much less strange and unlikely to others who have seen, as I have done, an Amœba, or an Actinophrys-like body, originate from the progressive molecular modifications taking place in a mass of chlorophyll and protoplasm within the filament of an alga. Many independent observers have watched all the stages of this process, and some have even seen Ciliated Infusoria originate by such a metamorphic change.] And, moreover, as I have myself ascertained, if one takes healthy-looking epithelial scales scraped from the inside of the mouth, which appear to contain nothing but the finest granules, and places them with a little saliva in a “live-box” (and this within a damp chamber kept at a temperature of about 90° Fahr.), in the course of from 5 to 10 hours, the cells may be found to be studded throughout with motionless Bacteria. Of course it may be said that the granules originally seen in the cells were offcasts from pre-existing Bacteria[8 - Or offcasts from pre-existing fungi, – constituting the “micrococci” of Professor Hallier.] which had gained access to the cell. And although, to many, this may seem an extremely improbable supposition, it is, nevertheless, one which it would be very difficult to disprove. The improbability of the notion is increased, moreover, when we find that Bacteria, and even Torulæ, will develop just as freely within closed cells taken from the very centre of a vegetable tuber, as they will in the midst of the more solid epithelial cell from the inside of the mouth. If it be urged that in this latter situation, there is the greatest chance of the cells being brought into contact with Bacteria, and that it must be considered possible for imaginary minute offcasts from these Bacteria to make their own way into the substance of the epithelial cell, I am quite willing to grant the desirability of taking such possibilities into consideration. But, at the same time, it seems all the less likely that the actual occurrence of the Bacteria is explicable on these grounds, because we find them developing just as freely within the cells freshly cut from the centre of a tuberous root, or we may find them already developed within these cells, if the root has begun to decay. To suppose that actual germs of Bacteria and of Torulæ are uniformly distributed throughout the tissues of higher organisms, is to harbour a hypothesis which would appear to many to be devoid of all probability – more especially when the heterogenetic mode of origin of larger and higher organisms is a matter of absolute certainty.

3. Origin of Bacteria and of Torulæ by Archebiosis

The evidence on this part of the subject is, I think, sharply defined and conclusive. Simple experiments can be had recourse to, which are not admissible in the discussion of the question as to the origin of Bacteria and Torulæ by Heterogenesis. There, we wish to establish the fact that living matter is capable of undergoing a certain metamorphosis, and consequently, we must deal with living matter. Here, however, with the view of establishing the fact that living matter can arise de novo, if we are able, shortly after beginning our experiment, to arrive at a reasonable and well-based assurance that no living thing exists in the hermetically sealed experimental vessel – if the measures that we have adopted fully entitle us to believe that all living things which may have pre-existed therein have been killed – we may feel pretty sure that any living organisms which are subsequently found, when the vessel is broken, must have originated from some re-arrangements which had taken place amongst the not-living constituents of the experimental solutions, whereby life-initiating combinations had been formed.

The possibility of the de novo origination of Bacteria, Torulæ, and other such organisms, is one which is intimately associated with the doctrine as to the cause of fermentation and putrefaction. With regard to the almost invariable association of such organisms with some of these processes, almost all are agreed. There is, moreover, a very frequent association of particular kinds of organisms with particular kinds of fermentation. Hence the assumption is an easy and a natural one to many persons, that the organisms which are invariably met with in some cases are the causes of these fermentations,[9 - From this view the transition is also easy, though none the less illegitimate, to the doctrine that all fermentations are caused by organisms; just as it has been easy to start, and find converts for, the doctrine expressed by the phrase “omne vivum ex vivo.” The distinction between all and some is only too often overlooked.] although it is quite obvious that the facts on which this view is based, are equally explicable on the supposition that the organisms are concomitant results or products (due to new chemical combinations) of the fermentative changes. In the one case the fermentative changes are believed to be initiated by the influence of living organisms; and those who regard living things as the only true ferments, for the most part also believe that living things are incapable of arising de novo. They think that those organisms which serve to initiate the changes in question, have been derived from a multitudinous army of omnipresent atmospheric germs, which are always ready, in number and kind suitable for every emergency. This is the doctrine of M. Pasteur and others. On the other hand, fermentations and putrefactions may be regarded as sets of chemical changes, which are apt to occur in organic and other complex substances – these changes being due either to the intrinsic instability of the body which manifests them, or to molecular movements communicated to it by a still more unstable body. Baron Liebig says: – “Many organic compounds are known, which undergo, in presence of water, alteration and metamorphosis, having a certain duration, and ultimately terminating in putrefaction; while other organic substances that are not liable to such alteration by themselves, nevertheless, suffer a similar displacement or separation of their molecules, when brought into contact with the ferments.”

Each substance belonging to the first class, would be at the same time, therefore, both ferment and fermentable substance; whilst a small portion of such substance, when brought into contact with a less unstable substance, might induce such molecular movements as to make it undergo a process of fermentation. With regard to the cause of such induced fermentative changes, Gerhardt[10 - ‘Chimie organique,’ 1856, t. iv. p. 589.] says, in explaining Liebig’s views: – “Every substance which decomposes or enters into combination is in a state of movement, its molecules being agitated; but since friction, shock, mechanical agitation, suffice to provoke the decomposition of many substances (chlorous acid, chloride of nitrogen, fulminating silver), there is all the more reason why a chemical decomposition in which the molecular agitation is more complete, should produce similar effects upon certain substances. In addition, bodies are known which when alone are not decomposed by certain agents, but which are attacked, when they exist in contact with other bodies incapable of resisting the influence of these agents. Thus platinum alone does not dissolve in nitric acid, but when allied with silver, it is easily dissolved; pure copper is not dissolved by sulphuric acid, but it does dissolve in this when it is allied with zinc, &c. According to M. Liebig it is the same with ferments and fermentable substances; sugar, which does not change when it is quite alone, changes – that is to say ferments – when it is in contact with a nitrogenous substance undergoing change, that is, with a ferment.”

Thus, in accordance with this latter view, living ferments are not needed – mere dead, organic or nitrogenous matter suffices to initiate the processes in question.[11 - Those who hold this opinion do not of course deny that living ferments can initiate fermentations. Every-day experience convinces them of the truth of this. They merely affirm that the intervention of vital action is not essential: they look upon fermentation as a purely chemical process, and believe that even in those cases where fermentation is initiated by living organisms (such as beer-yeast), these – although living – act chemically upon the matter which undergoes fermentation.] Those who hold this opinion may or may not believe that organisms are capable of arising de novo;[12 - They may not believe this, because they may be unaware of the fact of the invariable association of some organisms with some kinds of fermentations, and may consequently have never concerned themselves with the evidence bearing upon this part of the question. (See Gerhardt, loc. cit.)] though there can be little doubt that a belief in the truth of such a doctrine does, almost inevitably, entail a belief in the de novo origination of living things. No one who has looked into the evidence, doubts the fact of the association between some of these processes and the presence of organisms; the only question is, as to the relation in which they stand to one another. If organisms are not the causes of those fermentative changes with which they are invariably associated, then they are, in all probability, the results of such changes; and they must certainly have been produced de novo if it can be shown that fermentation or putrefaction may take place under the influence of conditions which make it certain that pre-existing living organisms could have had nothing to do with the process.

Now, in order to lend some air of probability to the former hypothesis, concerning the necessity for the existence of living ferments, it was incumbent upon its supporters to endeavour to show that the air did contain such a multitude of “germs,” or living things, as were demanded by the requirements of their theory. Spallanzani and Bonnet had, as far as the imagination was concerned, done all that was necessary. They had proclaimed the universal diffusion of “germs” of all kinds of organisms throughout the atmosphere – which were ready to develop, whenever suitable conditions presented themselves. So far, however, this was but another hypothesis. To establish the doctrine that fermentation cannot take place without the agency of living ferments, we cannot receive hypotheses in evidence: facts are needed. These, no one attempted to supply in an adequate manner[13 - M. Pouchet and others had examined the dust which settles on objects, and amongst much débris of different kinds had found comparatively few ova or spores. He had not, however, up to this time, filtered the air, so as to see what germs might be detected floating about in the atmosphere.] anterior to the investigations of M. Pasteur. Speaking of his researches, even M. Milne-Edwards says,[14 - ‘Anat. et Physiol. compar.’ t. viii. p. 264.] “Previous to this time, the existence of reproductive particles, or infusorial germs in the atmosphere was nothing more than a plausible hypothesis, put forward in order to explain the origin of such creatures in a manner conformable with the general laws of reproduction; but it was only a mere supposition, and no one had been able actually to see or to handle these reproductive corpuscles.”

We have to look, therefore, to M. Pasteur’s investigations, and to others which may have been since conducted, for all the scientific evidence in support of what has been called the “Panspermic hypothesis.”

By an ingenious method of filtration, which is fully described in his memoir,[15 - ‘Annales de Chimie et de Physique,’ 1862, t. lxiv. p. 24.] M. Pasteur separated from the air that passed through his apparatus the solid particles which it contained. This search convinced him that there were, as he says, “constantly in ordinary air a variable number of corpuscles whose form and structure declare them to be organized.” Some of these, he thinks, resemble the spores of fungi, and others the ova of ciliated infusoria, though he adds: – “But as to affirming that this is a spore, much less the spore of any definite species, and that one is an egg, and belonging to such an infusorium, I believe that this is not possible.” He limits himself, in fact, to the statements, that the corpuscles which he found, were (in his opinion) evidently organized; that they resembled in form and appearance the germs of the lower kinds of organisms; and that, from their variety in size, they probably belonged to many different sorts of living things. Even here, therefore, we have to do with the impressions of M. Pasteur, rather than with verified statements. All that has been established by his direct investigation as to the nature of the solid bodies contained in the atmosphere is this: that the air contains a number of round or ovoidal corpuscles, often quite structureless, which he could not distinguish from the spores of fungi[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.]– some of which, being about the right size, were round or ovoidal, and structureless. In addition, however, it has been shown that the air contains other rounded corpuscles which are similarly structureless, though composed of silica or starch. It may therefore be asked, in the first place, whether the conclusion is a sufficiently safe one that many of the corpuscles found by M. Pasteur were spores of fungi; and in the next place, supposing this to have been established, whether such spores were living or dead. These questions would have been answered satisfactorily if M. Pasteur could state that he had actually watched the development of such corpuscles, in some suitable apparatus, into distinct organisms. But any such development, he distinctly states, he never witnessed. He says[17 - Loc. cit. p. 34, note 1.]: – “What would have been the better and more direct course would have been to follow the development of these germs with the microscope. Such was my intention; but the apparatus which I had devised for this purpose not having been delivered to me at a convenient time, I was diverted from this investigation by other work.” The evidence which he does adduce, in subsequent portions of his memoir, in order to prove that some of these corpuscles were really “fertile germs,” is almost valueless, because all the facts are open to another interpretation, which is just as much, nay, even more, in accordance with Baron Liebig’s than with his own doctrine of fermentation.

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 - Loc cit. p. 56.] 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.”

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 - See p. 57.] 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 - M. Pasteur’s use of this term, in which he is followed by others holding similar opinions, is much to be deprecated. Having said that he had found certain corpuscles which resembled spores of fungi, or ova of infusoria, he subsequently speaks of them as “germs,” and also applies the same name to the reproductive particles of Bacteria, which he merely assumes to be present in the atmosphere. Thus, having only proved that corpuscles resembling spores of some fungi, are to be found in the atmosphere, he subsequently speaks of the presence of a multitude of atmospheric germs as an established fact, without at all prominently pointing out that, so far as the most important of these are concerned – germs of Bacteria– their existence had only been inferred, and not proved.] 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.

Although, therefore, no direct evidence has been adduced tending to show that Bacteria are present in the atmosphere, even if this evidence had been forthcoming, it would have been necessary, in reference to M. Pasteur’s hypothesis, for it to be supplemented by further evidence to the effect that Bacteria were well capable of resisting such an amount of desiccation as must have been involved by their presence for an indefinite time in the atmosphere even of the hottest and driest regions of the earth. For, organic substances in solution do not only putrefy in moist weather or moist climates; they putrefy most rapidly and surely when the temperature is high, and quite irrespectively of the amount of moisture contained in the atmosphere. A property of resisting the effects of desiccation – the possession of which, by Bacteria, is so necessary for the truth of M. Pasteur’s argument – ought to have been shown by scientific evidence to be a real attribute of such organisms; though it seems, on the contrary, to have been assumed to exist, with almost equal readiness by both parties, in the controversies concerning the possibility of “spontaneous generation.” This error may be ascribed to the misguiding influence of a treacherous analogy. Whilst it may be true that certain seeds and spores, and also that Rotifers, “Sloths,” and some Nematoids are capable of resisting the influence of a prolonged exposure to desiccating influences, it may well be asked, whether the same fact necessarily holds good for organisms such as Bacteria, which have no chitinous or other envelopes to protect them, and which are merely minute fragments of naked protoplasm. Having elsewhere[21 - ‘Philosophical Transactions,’ 1866, pp. 616–619.] shown how far presumptions had stolen a march upon established facts, in reference to the supposed possession of a similar property by the Free Nematoids, my eyes were opened to the reality of this uncertainty with regard to Bacteria. It is, however, no easy matter definitely to prove or to disprove the possession of this property by organisms so minute as Bacteria, and therefore so difficult to identify. If dried Bacteria are added to a drop of a suitable solution – similar to that in which they had been bred – it soon becomes quite impossible to distinguish those which have been added from those which arise in the fluid. Taking into consideration the fate of other simple organisms, however, it is by no means improbable that they should be killed even by a short desiccation. I have found, for instance, that desiccation for half-an-hour in a room at a temperature of 65° F. suffices to kill all the larger, naked, lower organisms with which I have experimented – including long Vibrios, Amœbæ, Monads, Chlamydomonads, Euglenæ, Desmids, Vorticellæ and all other Ciliated Infusoria.

But, certain indirect evidence seems to speak most authoritatively against the supposition that the air contains any notable quantity of living Bacteria, or Bacteria germs, whether visible or invisible. I have always found that a simple solution of ammonic tartrate, which has been placed – without previous boiling – in a corked bottle of greater capacity, will become turbid in two or three days, owing to the presence of myriads of Bacteria; whilst a similar solution, previously boiled, may remain for ten days, three weeks, or more, without showing the least trace of turbidity, although the open neck of the bottle or flask in which it is contained, may be covered only by a loose cap of paper. And yet, at any time, in order to make this fluid become turbid in from 24 to 48 hours, all that one has to do is to bring it into contact with a small glass rod which has just been dipped into a solution containing living Bacteria.[22 - The solution, during the whole time, being exposed to a temperature of 75° to 85° F.]

If we find that an eminently inoculable fluid will remain for two or three weeks, or perhaps more, in contact with the air without becoming turbid, though it will always become turbid in two or three days if brought into contact with living Bacteria, what can we conclude, but that living Bacteria are not very common in the atmosphere? These most striking facts can be easily verified by other observers.

Thus we find ourselves, at present, in this position. After all that has been said and done to prove the wonderful prevalence of “germs” in the atmosphere, we are really still in the region of hypothesis – no further advanced than we were in the time of Bonnet and of Spallanzani, so far as it concerns the organisms which are all important —Bacteria. Neither these nor their germs have been shown to exist in any recognizable abundance in the atmosphere, and yet in most fermentations they are the first organisms which display themselves; whilst in many such fermentations Bacteria alone occur. Nay more, even were they present in any great abundance, there is some reason to believe that the majority of them would exist as mere dead, organic particles – because Bacteria are more than likely to be unable to resist anything like an extreme or prolonged exposure to desiccating influences.

The first and essential data in support of M. Pasteur’s hypothesis must, therefore, be regarded as entirely unproved in respect to Bacteria– which are the most important of all organisms, in relation to the cause of fermentation and putrefaction.

Without the aid of elaborate experiments, however, the evidence which the microscope can supply is capable of leading us to the conclusion that such search for atmospheric Bacteria germs, was comparatively useless. If it can be shown that Bacteria can arise in a fluid independently of visible germs, then, obviously, any inquiries as to the nature of the visible contents of the atmosphere, can have only a very indirect bearing upon the question as to the mode of origin of these organisms. And yet by the aid of the microscope, as I have elsewhere stated, one can watch the appearance of almost motionless specks, more or less uniformly diffused through a motionless film of fluid, and can see them gradually develop into moving Bacteria or into Torulæ. So that, where no visible germs previously existed, visible particles of living matter develop, and more or less rapidly grow into distinct Bacteria. This may be best seen in a drop of a fresh and very strong turnip infusion, which has been filtered several times through the finest paper. The drop, placed in a live-box, should be flattened into a thin film by the application of the cover.

Thus protected, evaporation takes place very slowly, and with the live-box resting on one of Stricker’s hot-water plates, at a temperature of 85° to 90° F., and the latter upon the stage of the microscope, one can easily select a portion of the field in which either no particles or only a countable number exist. If, therefore, around and between any mere granules which may pre-exist, or in a clear space, one gradually sees in the course of two or perhaps three hours, a multitude of almost motionless specks (at first about 1/100000″ in diameter) in positions where no such specks previously existed; and if these specks may be seen gradually to increase in size and develop into Bacteria and Torulæ, then, at all events, we are able to say that these organisms can be developed without pre-existing visible germs, and we have just the same amount of actual evidence for believing that they have been formed de novo, as we should have for believing that crystals had been formed de novo, if we had seen them appearing under our eyes in the same manner. Whether they really arise after the fashion of crystals, without the aid of pre-existing though invisible germs, is a matter which can only be settled inferentially, by a subsequent resort to strict methods of experimentation.

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.

Some of the experiments by which he endeavoured to substantiate this position were of a very simple nature. Their narration attracted much attention at the time, as it was supposed that by their means M. Pasteur had – as he professed – conclusively shown the erroneousness of the views of those who believed in what was called “spontaneous generation.” These experiments were soon repeated by other observers, who, using different fluids, obtained quite opposite results. Thus it became obvious to impartial critics, that whilst the means adopted by M. Pasteur might be adequate to check the processes of fermentation or putrefaction in certain fluids, they were quite powerless to effect this when many other fluids were employed.

These particular experiments, however, still seem to exercise a very great influence on the minds of many in this country, who are either unaware of, or disbelieve in, the possibility of obtaining opposite results.

The chapter in which M. Pasteur detailed these experiments is thus entitled: – “Another very simple method of demonstrating that all the organized products of Infusions (previously heated) owe their origin to the corpuscles which exist suspended in the Atmosphere.” Whilst claiming to have already rigorously established the validity of this conclusion by the experiments described in previous chapters, M. Pasteur adds: – “If there remained the least doubt on this subject, in the mind of the reader, it would be dissipated by the experiments of which I am now about to speak.” (p. 66.)

Sweetened yeast-water, urine, infusions of pear and of beetroot, were placed in flasks with long necks, variously drawn out and bent. The flasks were subsequently treated as follows. M. Pasteur says: – “I then raise the liquid to the boiling-point for several minutes until steam issues abundantly from the extremity of the drawn-out neck of the flask, which is permitted to remain open. I then allow the flask to cool. But, singular fact – and one well calculated to astonish every one acquainted with the delicacy of the experiments relating to what is called ‘spontaneous generation’ – the liquid of this flask will remain indefinitely without alteration. The flask may be handled without any fear, it may be transported from place to place, allowed to experience all the seasonal variations of temperature, and its liquid does not undergo the slightest alteration, whilst it preserves its odour and its taste.” If, however, the neck of one of these flasks be broken off close to the flask itself, then, according to M. Pasteur, the previously unaltered fluid will, in a day or two, undergo the ordinary changes, and swarm with Bacteria and Mucedineæ.

“The great interest of this method is,” M. Pasteur adds, “that it completes, unanswerably, the proof that the origin of life in infusions which have been raised to the boiling point, is solely due to the solid particles[23 - As expressed, the proposition may be an approximation to the truth. M. Pasteur, however, really endeavours to lead his readers to believe that the “solid particles” which are efficacious, are, in all cases, living “germs.”] which are suspended in the air.” He believes that any living things pre-existing in the fluid itself would be destroyed by the high temperature to which it had been raised; and that those contained in the air of the flask would also be destroyed, if not expelled, by the process of ebullition. Believing that the air is the source of germs from which Life is first developed in infusions, he thinks that what rapidly enters at first, on the cessation of ebullition, has its germs destroyed by contact with the almost boiling liquid; whilst the air which enters subsequently, and more slowly, is supposed to deposit its germs in the various flexures of the tubes, so that none are able to reach the fluid itself. Infusions, thus protected, do not undergo putrefaction, says M. Pasteur, because the access of pre-existing living things is necessary for the initiation of this change, and such access is prevented by the tortuous and bent neck of the flask.

Others say that some fluids submitted to the conditions mentioned, will undergo putrefactive changes, and that, therefore, these experiments of M. Pasteur are utterly incapable of settling the general question as to the cause of fermentation and putrefaction, and also that concerning the origin of Life. Although acknowledging a certain difficulty in explaining the results which are sometimes attained by this method, some of us would rather confess this than confidently offer explanations – as M. Pasteur did – which may in a short time be stultified by the results of other experiments with different fluids.

Having previously shown[24 - ‘Nature,’ 1870, No. 36, p. 193.] that living things could appear and multiply in such a flask as M. Pasteur describes – in any flask, in fact, – which had been hermetically sealed during the ebullition of a suitable fluid within; this was deemed to be a result so contradictory to the explanations of M. Pasteur, that it appeared needless to add my testimony, as I could have done, to that of M. Victor Meunier and others, as to the different results obtainable by operating, in M. Pasteur’s fashion, with different fluids. It seemed to me that if organisms were to be procured in flasks from which air had been altogether expelled, it was useless still to urge the preservative virtues of any process of filtration of air – with the object of showing that living things in infusions derived their origin from atmospheric germs. Obviously, if there were no atmosphere, there could be no atmospheric germs present; and if living things were, nevertheless, developed under these exclusive circumstances, how could M. Pasteur or his disciples still expect to convince others that the first living things in infusions always proceeded from pre-existing atmospheric germs – even although it could be shown, that in many cases, when these were filtered off by flasks with narrow and tortuous necks, no living things were developed in such fluids. Granting to the full the truth of such facts, they could do nothing to establish the doctrine of the origin of infusorial life from pre-existing atmospheric germs, so long as it could also be shown that living things might be developed in boiled solutions to which air, instead of being filtered, was never allowed to enter at all.

It is not, therefore, because I think that some of the experiments which will subsequently be related afford any stronger or more direct support to my own conclusions, but because I think they may do this indirectly – by shaking the faith of many in some of the reasonings of M. Pasteur – that I am induced to give an account of them.[25 - If his reasonings can be shown to be quite inconclusive, and if his results can be otherwise explained, some people may, at last, begin to recognize that their blind and mistaken faith in M. Pasteur’s work has been somewhat misplaced.]

What has been hitherto said, also applies to the more recent statements concerning the efficacy of cotton-wool as an agent for filtering germs from the atmosphere. Prof. Huxley says he has never seen putrefaction or fermentation occur after certain organic fluids have been boiled for ten or fifteen minutes, if a good plug of cotton-wool has been inserted into the neck of the flask in which they are contained whilst ebullition is going on, and has, subsequently, been allowed to remain in the same situation. Using other or perhaps stronger fluids, however, I have found that such a method of proceeding is by no means adequate to stop the growth and development of organisms. And, also, even if it had been always efficacious – the reason adduced could not hold good, in the face of my other experiments, which had shown that a development of life might go on in cases where the air, which had been similarly driven out, was subsequently, in place of being filtered, prevented from gaining access to the fluid.

If germs derived from the air are the sole causes of putrefaction, then, surely, deprivation from air ought to be just as efficacious as any process of filtration of air – more especially when the filtration or the deprivation have a common starting point. And the mode of procedure, in both cases, is precisely the same up to a certain point. A fluid is boiled for a short time in order to kill the germs which may be within the flask, and to expel its previously contained air. At a certain stage of the ebullition, this may be arrested, if we have to do with a bent-neck flask, or one whose neck is plugged with cotton-wool, and no change, it is said, will subsequently take place in the contained fluid, because the air which enters is, by either of these means, filtered from its germs. But if, whilst ebullition continued, the neck of the flask had been hermetically sealed – so as altogether to prevent the re-ingress of air – and if the fluid, thus contained in vacuo, would nevertheless undergo fermentation, obviously the former explanation must be altogether shelved.

In the face of M. Pasteur’s explanations, and those of Professor Huxley, these frequent positive results with fluids contained in vacuo are absolutely contradictory. There may naturally arise, therefore, a very grave doubt as to the validity of the explanation adduced by M. Pasteur, and adopted by Professor Huxley and others.

All these experiments to which I have been alluding are based upon the supposition (assented to by Pasteur and Huxley) that Bacteria which pre-existed in the solution would certainly be destroyed by its being raised for a few minutes to a temperature of 212° F. This conclusion is, I believe, perfectly correct,[26 - M. Pasteur attempted to make a distinction in the case of slightly alkaline or neutral fluids (loc. cit., pp. 60–65). I have endeavoured to show the untenability of his conclusion in ‘Nature,’ 1870, No. 37, pp. 224–227.] and in support thereof I will adduce the following additional information.

Limits of ‘Vital Resistance’ to Heat displayed by Bacteria and Torulæ

After stating elsewhere[27 - ‘Nature,’ 1870, No. 35, p. 171.], that Vibriones are partly broken up or disintegrated by an exposure for a few minutes to a temperature of 212° F. in an infusion which is being boiled, and also that, in all probability, the life of Bacteria would be destroyed by such a treatment, I made the following remarks: – “With reference to these organisms, however, one caution is necessary to be borne in mind by the experimenter. The movements of monads and Bacteria may be, and frequently are, of two kinds. The one variety does not differ in the least from the mere molecular or Brownian movement, which may be witnessed in similarly minute, not-living particles immersed in fluids. Whilst the other seems to be purely vital – that is, dependent upon their properties as living things. These vital movements are altogether different from the mere dancing oscillations which not-living particles display, as may be seen when the monad or Bacterium darts about over comparatively large areas, so as frequently to disappear from the field. After an infusion has been exposed for a second or two to the boiling temperature, these vital movements no longer occur, though almost all the monads and Bacteria may be seen to display the Brownian movement in a well-marked degree. They seem to be reduced by the shortest exposure to a temperature of 100 °C. to the condition of mere not-living particles, and then they become subjected to the unimpaired influence of the physical conditions which determine these movements.” I now have various facts to add in confirmation of these conclusions, and in extension of our knowledge concerning the vital resistance to heat of Bacteria and Torulæ.

It would be a most important step if we could ascertain some means by which these primary movements of living Bacteria might be distinguished from the secondary, or communicated, movements of not-living particles. In many cases, organisms that are truly living may only exhibit very languid movements, which, as movements, are quite indistinguishable from those that the same Bacteria may display when they are really dead. Because the movements, therefore, are of this doubtful character, persons are apt, unfairly, to argue that the Bacteria which present them, are no more living than are the minute particles of carbon obtained from the flame of a lamp, which may exhibit similar movements. This, however, is a point of view which becomes obviously misleading if too much stress is laid upon it; and it is more especially so in this case, when those Bacteria which display the most characteristic sign of vitality – viz., “spontaneous” division or reproduction – do, at the time, almost always exhibit only the same languid movements. Mobility is, in fact, not an essential characteristic of living Bacteria, whilst the occurrence of the act of reproduction is the most indubitable sign of their life. It should be remembered, therefore, that any Bacteria which are almost motionless, or which exhibit mere Brownian movements, may be living, whilst those which spontaneously divide and reproduce, are certainly alive – whatever may be the kind of movement they present.

In any particular case, however, can we decide whether Bacteria, that have been submitted to a given temperature, and which exhibit movements resembling those known as Brownian, are really dead or living? If the movements are primary, or dependent upon the inherent molecular activity of the organism itself, they ought, it might be argued, to continue when the molecules of the fluid are at rest; if, on the other hand, they are mere secondary or communicated movements, impressed upon the organisms as they would be upon any other similarly minute particles, by the molecular oscillations of the fluid in which they are contained, then the movements ought to grow less, and gradually cease, as the fluid approaches a state of molecular rest – if this be attainable. Following out this idea, some months ago, I first tested the correctness of the assumption by experimenting with fluids containing various kinds of not-living particles; such as carbon-particles from the flame of a lamp, or freshly precipitated baric sulphate. However perfect may have been the Brownian movements when portions of these fluids were first examined beneath a covering-glass, they always gradually diminished, after the specimen had been mounted by surrounding the covering-glass with some cement or varnish. Thus prepared, no evaporation could take place from the thin film of fluid, and after one, three, four, or more hours – the slide remaining undisturbed – most of the particles had subsided, and were found to have come to a state of rest. In order still further to test these views, I took an infusion of turnip, containing a multitude of Bacteria whose movements were of the languid description, and divided it into two portions. One of these portions was boiled for about a minute, whilst the other was not interfered with. Then, after the boiled solution had been cooled, a drop was taken from each and placed at some little distance from one another on the same glass slip; covering-glasses half an inch in diameter were laid on, and the superfluous fluid beneath each was removed by a piece of blotting-paper. When only the thinnest film of fluid was left, the covering-glasses were surrounded by a thick, quickly-drying cement.[28 - I always employ a solution of gum mastic and bismuth in chloroform. If a different varnish be employed, it is of course necessary to ascertain whether its application is injurious to the enclosed Bacteria.] Examined with the microscope immediately afterwards, it was generally found that the Bacteria which had been boiled presented a shrunken and shrivelled aspect – whilst some of them were more or less disintegrated – though, as far as movement was concerned, there was little to distinguish that which they manifested, from that of their plumper-looking relatives which had not been boiled.