The modes of origin of lowest organisms

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 particles23 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 shown24 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

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 and in support thereof I will adduce the following additional information.

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

After stating elsewhere27, 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 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.

If the specimens were examined again after twenty-four or more hours, there was still very little difference perceptible between them, as regards their movements. And the same was the case when the specimens were examined after a lapse of some days or weeks. One important difference does, however, soon become obvious. The Bacteria which have not been boiled, undergo a most unmistakeable increase within their imprisoned habitat; whilst those which have been boiled, do not increase. The two films may be almost colourless at first (if the Bacteria are not very abundant), but after a few days, that composed of unboiled fluid begins to show an obvious and increasing cloudiness, which is never manifested by the other. Microscopical examination shows that this cloudiness is due to a proportionate increase in the number of Bacteria.

Is the continuance of the movements of the organisms which had been boiled attributable to their extreme lightness, and to the slight difference between their specific gravity and that of the fluid in which they are immersed? I soon became convinced that this was one, if not the chief reason, when I found that Bacteria which had been submitted to very much higher temperatures, behaved in precisely the same manner as those which had been merely boiled, and also that other particles which – though obviously dead – had a similar specific lightness, also continued to exhibit their Brownian movements for days and weeks. This was the case more especially with the minute fat particles in a mounted specimen of boiled milk,29 and also with very minute particles which were gradually precipitated30 from a hay infusion that had been heated to 302° F. for four hours. Trials with many different substances, indeed, after a time convinced me that the most rapid cessation of Brownian movements in stationary films,31 occurred where the particles were heavy or large; and that the duration of the movement was more and more prolonged, as the particles experimented with, were lighter or more minute. So that, when we have to do with Bacteria, the minute oil globules of milk, or with other similarly light particles, the movements continue for an indefinite time, and are, in part, mere exponents of the molecular unrest of the fluid. They are always capable of being increased or renewed by the incidence of heat or other disturbing agencies.