CHAPTER VII.

CONTAGIOUS POISONS, COMPARED WITH YEAST—DOES THAT AGENT ASSUME THE AERIFORM STATE?

Lest the evidence we have laid before the reader should not be so satisfactory and conclusive as it has been deemed by us, the details and results of some investigation into yeast will now be given.

It occurred to us, that it would be useful, in our inquiry respecting contagious poisons, to ascertain whether or not yeast was capable of producing its wonted effects through the medium of the air, if, in short, it was capable of taking on the vaporic state. We were led to this inquiry from the consideration, that it and contagious poisons presented points of resemblance of the most important nature, and that the history of the one might elucidate that of the others.

Yeast is the only other inanimate substance, besides the contagious poisons, with which we are acquainted, which has the property of producing a substance in every respect like itself, in short, of reproduction.

Like the contagious poisons, too, it is the result of a great and active process, which, like them, it can again produce in other materials.

Fermentation may be likened to contagious disease, and, indeed, it is not the first time contagious disease has been likened to fermentation. These diseases produce contagious poisons,—fermentation produces yeast, and again, these agents produce their respective processes.

Bodies in general, which have undergone the action at least of the active contagious poisons, are not liable to be again affected by them; so vegetable bodies, which have undergone fermentation, by means of yeast, are not liable to be again acted upon by a second application.

It is important to know if yeast is capable of assuming the aeriform state.

It is a complex substance, being compound in its chemical constitution. Did we find that it was, then it might seem probable that contagious poisons (putting out of consideration the evidence already given), might possibly be so disseminated also. It runs readily into putrefaction, and in a short time loses its power of producing its peculiar effects, that is, fermentation.

Knowing this, we were inclined to believe that it could not get into the atmosphere otherwise than in a decomposed state, and, therefore, could not act through that medium.

The question was put to a most intelligent brewer, conversant with its common qualities, and the unhesitating answer was immediately given, that it could act through the air.

Here we could not help marking the striking similarity in the bearing of the brewer, with the confidence with which medical men speak of the like property of contagious poisons—the marked taking for granted _what_ was opposed in both instances, to the obvious evidence of chemistry, and _what_ might be so readily tested by experiment.

He was of opinion, that if fermentation were going on in a tub in an apartment where there was a quantity of wort (liquid ready for fermentation), to which no yeast had been added, that that process would be excited from the yeast in the fermenting tub, producing its influence through the medium of the atmosphere, in short, by being dissolved in it.

As that opinion did not tally with our opinions on chemical affinity, recourse was had to experiment.

_1st_ EXPERIMENT.

A quantity of wort, to which no yeast had been added, was put into a wide mouthed vessel, and suspended in the mouth of a large tub, containing ale in an active state of fermentation. The vessel was allowed to remain three days, and at the end of that time no more appearance of fermentation was detected, than a very slight display of frothy bubbles in the middle, nothing more than we were assured by the brewer, was wont to appear from spontaneous fermentation.

A blind devotion to his opinion might have induced the brewer to attribute to the yeast acting through the medium of the air, what was quite spontaneous, and if he had done so, how like his case would have been to that of some medical men, who unwittingly attribute to atmospheric contagion, what is spontaneous or dependent on other agencies.

From this experiment it appears that yeast is incapable of solution in the air, and of producing through that medium its peculiar effects.

But to make the result still more certain, another experiment was performed.

_2d_ EXPERIMENT.

A wide mouthed vessel, containing a quantity of water, was suspended over some liquor, in a state of active fermentation, for the purpose of absorbing any gas or yeast, in a state of vapour proceeding from it. It was kept there two days, and then examined. Its taste was somewhat altered, and it had acquired a slight odour much resembling that of yeast, probably from the absorption of gas. It was thought, that if this water had become impregnated with yeast, that that circumstance would be rendered manifest, by producing fermentation, when added to a quantity of wort; and to determine the question, the following trial was made.

Two jugs half filled with wort, free from yeast, were placed in an apartment whose atmosphere was favourable to fermentation. To one was added the water which had been suspended over the fermenting tub, and to the other an equal quantity of pure water. They were then put aside, and secured from interference. At the end of three days they were examined. The wort to which had been added the water taken from over the fermenting tub, presented on its surface a few frothy bubbles, but not the slightest appearance of yeast.

The wort, to which pure water had been added, presented an appearance identically the same, having a few frothy bubbles on its surface, but not any other, the most trifling sign of fermentation.

Similar experiments were made at a distillery, where the facilities for their success were said to be even greater than at the brewery, and they were marked with precisely similar results.

Thus, then, it appears, as the result of experiment, that yeast is incapable of assuming the vaporic or aeriform state.

This inquiry will perhaps appear to many remote and unconnected with the proper subject of these pages, and, hence, that it is altogether superfluous; but we think differently, and are of opinion, that an accurate knowledge of that agent is calculated to be of the utmost use in forwarding the formation of a just estimate of the habitudes of the contagious poisons, which it resembles in several very important points.

It is, as before stated, the only other substance belonging to the inanimate world, whose immediate and most prominent property is that of propagating a substance identically the same—of producing, through a peculiar and uniform process, an agent possessed again of all its properties.

Some other agents may be said, under some circumstances, to propagate themselves, but it is in a very remote way, and by no means by that direct and uniform operation which marks the propagation of contagious poisons and yeast, which is obviously as well defined as germination among animal and vegetable bodies.

_Heat_, under some circumstances, does cause the production or evolution of heat, but that is rather an accidental circumstance, brought about remotely by the chemical operation produced, and would have taken place whatever had been the cause of that process, and is not the result of an immediate and particular property.

Vitiated air also is calculated much in the same way to reproduce itself; but, instead of being in virtue of a quality possessed by the palpable contagious poisons, vitiated air of itself produces disease, and a common result of disease is vitiated or impure air.

The close analogy subsisting between yeast and the palpable contagious poisons, it is hoped, has been fully made out; and though it is not permitted, by the rules of logic, positively to determine, that the laws which regulate the action of the one, necessarily hold with the other agents; yet, where there is no evidence of a contrary nature, the closeness of the connection lends countenance to the idea.

That analogy seems remarkably strong when it is considered, that both yeast and the palpable contagious poisons produce their peculiar effects only once upon the same object.

Many instances are known where the palpable contagious poisons have produced their peculiar effects more than once, but these deserve rather to be held as exceptions to the general law than as a proof against its existence.

PART II.