Although, therefore, there is a contradiction between the unwarrantable and ill-begotten formula, “omne vivum ex vivo,” and the doctrines of what has been called “Spontaneous Generation”; there is no contradiction whatever between such doctrines and the only generalization which we are really warranted in arriving at, to the effect that some representatives of every kind of organism are capable of reproducing similar organisms.
Bacteria, Torulæ, or other living things which may have been evolved de novo, when so evolved, multiply and reproduce just as freely as organisms that have been derived from parents.
The views as to the origin of Bacteria and Torulæ which are most worthy of attention, may be thus enumerated: —
a. That they are independent organisms derived by fission or gemmation from pre-existing Bacteria and Torulæ.
b. That they represent subordinate stages in the life-history of other organisms (fungi), from some portion of which they have derived their origin, and into which they again tend to develop.
c. That they may have a heterogeneous mode of origin, owing to the more complete individualization of minute particles of living matter entering into the composition of higher organisms, both animal and vegetal.
d. That they may arise de novo in certain fluids containing organic matter, independently of pre-existing living things (Archebiosis).
I shall make some remarks concerning each of these views, though the evidence I have to adduce mainly concerns the possibility of the origin of Bacteria and Torulæ in the way last alluded to, viz., by Archebiosis.
The third mode of origin is what is called Heterogenesis; whilst the first and second modes are the representatives of more familiar processes, included under the head of Homogenesis. Thus, in accordance with the first view, Bacteria may be regarded as low organisms having a distinct individuality of their own and multiplying by a process of fission – thus affording instances of what I propose to term direct Homogenesis. Whilst, in accordance with the second view, Bacteria are supposed to represent merely one stage in the life-history of higher organisms, which are therefore reproduced by an indirect or cyclical process of Homogenesis.
The possible modes of origin of Bacteria and Torulæ may, therefore, be tabulated as follows: —
I. Homogenetic Mode of Origin of Bacteria and Torulæ
Bacteria and Torulæ being already in existence, they may, undoubtedly, reproduce organisms similar to themselves by processes of fission and gemmation – in the same way that other low protistic organisms propagate their kind. Although so many reasons rendered this view probable, it was some time before I was able actually to confirm it by personal observations in the case of Bacteria. In the ordinary microscopical examination of portions of an infusion containing these organisms, an observer may watch for hours and never see a single instance of such fission occurring. His attention is apt to be distracted by the number of organisms which are constantly flitting before his view, and he is, moreover, perhaps apt to pay particular attention to those which seem by their movements to be most obviously alive.
I have observed the process most plainly when a few Bacteria have been enclosed in a single drop of fluid, pressed into a very thin stratum, in a “live-box” kept at a temperature of about 90° Fahr. by resting on one of Stricker’s warm-water chambers placed on the stage of the microscope. Under these conditions, I have seen a Bacterium of moderate size divide into two, and each of these into two others somewhat smaller, in the course of fifteen minutes.
It is still more worthy of remark, that in all cases (so far as I have been able to observe), this, the most certain sign of vitality which such organisms are capable of manifesting, is shown by those which, from their stillness, might be considered dead. The Bacteria which are about to divide are generally either motionless,1 or merely present slight oscillating movements. The separation is quickly brought about at the joint, so that the original organism divides into two equal portions; and these, lying close together, soon develop a new construction as they grow, through which a further division may occur.
That the Bacteria which reproduce should be in a comparatively quiescent condition, seems not difficult to understand. Such rudimentary organisms do not appear to possess cilia or other locomotory appendages: their movements are, therefore, in all probability dependent upon the mere molecular changes which are taking place within them, and upon which their life and nutrition depend. The process of fission must, however, be considered as the result of a new effort at equilibrium, which has, perhaps, been necessitated by molecular changes that have occurred during a preceding period of growth. The living matter which is no longer able to exist round a single centre, re-arranges itself around two centres, – as a result of which, fission occurs. It seems only natural, therefore, that whilst this active work of molecular re-arrangement is going on, those other molecular movements which occasion the actual locomotion of the organism from place to place, should be more or less interfered with.
This is the one and only mode of multiplication of Bacteria and of Torulæ which is actually known to occur; and such a limitation is in accordance with the more general fact, that processes of fission or gemmation are the only means of reproduction that are known to occur in the lower kinds of organisms, belonging to the PROTISTIC kingdom.
However well this process of fission may have been established, as a frequent mode of reproduction of Bacteria, such a fact does not lend any support to the notion that these are necessarily distinct and independent organisms. Torulæ (of which beer-yeast is the most familiar example) may similarly undergo this process of mere vegetative repetition to an indefinite extent, whilst only some of the products develop into fungi. The gonidia of lichens may also reproduce indefinitely in this fashion, and only some of the products of multiplication may go on to the production of lichens similar to that from which the gonidia had been derived.
It is a fact, however, admitted by many, and which any patient microscopist is capable of verifying for himself, that some Bacteria do develop into Leptothrix filaments, and that these are capable of passing into a dissepimented mycelial structure of larger size and undoubtedly fungus nature – from which fructification of various kinds may be produced. Some Bacteria may therefore develop into some fungi, just as certainly as some Torulæ may develop into other fungi, or, just as surely as some multiplying gonidia may develop into lichens.
In order to prove, however, that the Bacteria which happen to go through this development into Leptothrix and thence into fungi, are strictly to be considered as necessary links in the life-history of fungi, it would be essential for the person holding such views, to show that Bacteria could not arise independently – or at least that no independently evolved Bacteria could develop through Leptothrix-forms into a fungus. And, similarly, for the other kinds of organisms: in order to establish that the Torula cell is a necessary link in the life-history of certain fungi, or the gonidial cell a necessary link in the life-history of lichens, it would be necessary to show that Torulæ or gonidial cells could not originate de novo– that no independently evolved Torula or gonidial cell could develop into a fungus or a lichen.
An easier position to establish would be, that the Bacterium or the Torula were occasionally links in the life-history of fungi, or that the gonidial cell was an occasional link in the life-history of a lichen. This doctrine would leave the other more difficult problems, – as to the possible existence of supplementary modes of origin for such organisms by Heterogenesis or by Archebiosis – perfectly open questions.
To establish the position