Chapter V: Preface (4)

These facts are not so new and exceptional, however, as they may at first sight appear. It has been long known that a boiled fluid extremely prone to change, will not yield infusoria if the vessel in which it is contained is filled with the fluid. Burdach says[85]:--“Gruithuisen a reconnu que des infusions, même très fécondes d’ailleurs, celles du foin par exemple, ne donnaient point d’infusoires dans des flacons de verre dont le bouchon était assez enfoncé pour toucher à la surface de l’eau.” On the other hand, no experiments with which I am acquainted, in which heated fluids and calcined air have been shut up in closed flasks, have yielded so many positive results as those of Professor Wyman of Cambridge, U.S.,--and his were performed under precisely the reverse conditions. Large flasks were used, and only 1/15–1/20 of their bulk was filled by the experimental fluids.[86] Gruithuisen’s results were explained by Burdach on the ground that a certain amount of air was necessary, and it was also with the view of subjecting his fluids to as large an amount of air (calcined) as possible, that Professor Wyman employed small quantities of fluids in large flasks. These views were dictated by the chemical doctrines of Gay-Lussac and others, to the effect that the oxygen of the air is the initiator or _primum movens_ of fermentative changes.[87]

[85] ‘Traité de Physiologie.’ Translated by Jourdan. 1837. t. i., p. 18.

[86] ‘American Journal of Science,’ July, 1862.

[87] See Gerhardt’s, ‘Chimie Organique,’ t. iv. pp. 540 and 547.

Now, without doubting in the least that in some instances this may be the case, it seems to me quite obvious, from my own experiments, that a different interpretation may be given of Gruithuisen’s results--which I have myself verified,--and of the fact that meats and vegetables will often remain unchanged for years after having been heated in closed tins from which all air has been expelled.[88]

[88] It was, indeed, the consideration of these latter facts which originally forced Gay-Lussac to the conclusion, that fermentation would not take place _in vacuo_, or without the presence of free oxygen, which was and still is, believed by many, to be the immediate determining cause of fermentation.

If we ponder only upon the fact that certain fluids, in contact with a very small quantity of air, in an hermetically-closed vessel, will not undergo change; though these same fluids will change when exposed to a much larger quantity of calcined air, there may be strong reason for coming to an opinion similar to that of Gay-Lussac. When, however, it is also ascertained that provisions which have been subjected to the long-continued influence of heat, do not undergo change in closed vessels, if all air has been expelled from the _very small space above the level of the provisions_; though many organic infusions will putrefy if they occupy only one half, or less, of a hermetically closed vessel from which all air has been similarly expelled by ebullition of its fluid contents, it is impossible that the same explanation can hold good. And at the same time another interpretation is suggested for the first set of facts.

The last-mentioned experiments prove[89] that fermentation can take place _in vacuo_, when the conditions are more favourable than those which present themselves within the almost full tins containing provisions. The change in these latter cases cannot (in the great majority of instances) proceed far[90], because there is no adequate space into which residual gases may be emitted. When this emission (which is almost always one of the accompaniments of a fermentative change) has taken place to a slight extent, the meats are in the very best condition for preservation. There is an utter absence of light, an absence of free oxygen, and also an absence of that diminished pressure which my experiments seem to show is favourable to the promotion of many kinds of fermentative change. So that if fermentation does not take place in a closed flask which is _full_ of a boiled infusion of hay,[91] it may be owing to the fact that there is no space for the residual gases, and that undue pressure retards many fermentative changes. This is also perfectly compatible with the other fact that the same kind of fluid will undergo change when a small quantity of it is contained in a comparatively large flask--owing to there being, in such a case, plenty of room for residual gases to be effused, before that undue amount of pressure is brought about, in the presence of which such a fluid will no longer ferment or putrefy. Fluids, therefore, whose putrefaction is hindered by increased pressure and favoured by diminution of pressure, may be placed under conditions which are successively more favourable than the last, by putting a gradually smaller and smaller quantity of fluid into a flask, to which calcined air is admitted, and, better still--if the stimulus of oxygen is not absolutely needed in order to incite fermentation in the fluid employed--by only half filling the flask, and procuring a more and more perfect vacuum.

[89] This proof is more severe in certain other experiments (not yet published) in which I had the benefit of Professor Frankland’s assistance. The vacuum in these cases was perhaps more perfect, having been procured by means of a Sprengel’s pump and a simultaneous ebullition of the fluid, during which the flasks were hermetically sealed. The closed flasks were subsequently exposed to a temperature of 293° F. for a short time.

[90] An examination of tins of “perfectly good” meats has convinced me that a very small number of _Bacteria_ and _Leptothrix_ filaments are occasionally to be met with.

[91] It has, however, been ascertained by M. Pouchet, that beer-yeast, even after prolonged ebullition, will undergo change in a flask which is full and hermetically sealed; and the manufacturers of preserved meats also find that occasionally, in some of their best prepared tins, the meats become putrid, and that the putridity is accompanied by the presence of organisms. Some fermentations are doubtless attended by a less copious emission of waste gases than that which characterizes other fermentations; and some fermentations will progress in spite of a moderate amount of pressure.

In accordance with the doctrines of Baron Liebig, therefore, my experiments, as well as those of many other investigators, tend to show that fermentative and putrefactive changes are merely processes of chemical re-arrangement, which frequently take place--as it were “spontaneously”--owing to the inherent instability of certain nitrogenous compounds in the presence of free oxygen. My experiments have, however, also revealed the additional fact that, under the combined influence of heat and diminished pressure, some fluids will undergo fermentation even in closed vessels, from which all air has been expelled. They lend no support to the idea that the air is so thickly laden with _living germs_ as some would have us suppose; and in view of the mass of positive information now in our possession concerning the degree of heat which suffices to kill the lowest organisms, they also, as I think, entitle us to come to the conclusion that such organisms are (as the microscopical evidence might lead us to believe) really capable of being evolved _de novo_. These lowest organisms are, in fact, to be regarded as occasional concomitant products, rather than as invariable or necessary causes of all fermentative changes.

It would thus appear that specks of living matter may be born in suitable fluids, just as specks of crystalline matter may arise in other fluids. Both processes are really alike inexplicable--both products are similarly the results of the operation of inscrutable natural laws, and what seem to be inherent molecular affinities. The properties of living matter, just as much as the properties of crystalline matter, are dependent upon the number, kind, and mode of collocation of the atoms and molecules entering into its composition. There is no more reason for a belief in the existence of a special “vital force,” than there is for a similar belief in the existence of a special “crystalline force.” The ultimate elements of living matter are in all probability highly complex, whilst those of crystalline matter are comparatively simple. Living matter develops into Organisms of different kinds, whilst crystalline matter grows into Crystals of diverse shapes. The greater modifiability of living matter, and the reproductive property by which it is essentially distinguished from crystalline matter, seem both alike referable to the great molecular complexity and mobility of the former. Crystals are statical, whilst organisms are dynamical aggregates, though the evolution of both, marked by their peculiar characteristics, may be regarded as visible expressions testifying to the existence of one all-pervading Power

“Whose dwelling is the light of setting suns,
And the round ocean, and the living air,
And the blue sky, and in the mind of man:
A motion and a spirit that impels
All thinking things, all objects of all thought,
And rolls through all things.”

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