have paid attention to infusoria. I reserve, so far as it concerns me, the question of the identity or the difference of these species, and of the variety of their forms, subordinated to changes in the condition of the medium in which they live. I accept them provisionally such as they are described, and I arrive at the conclusion that these six species of vibrions are six species of animal ferments, and that they are the ferments of putrefaction. Besides this, I have shown that all these vibrions can exist without free oxygen, and that they perish in contact with this gas, if nothing preserves them from its direct action. The fact that I announced to the Academy two years ago, and of which I have recently pointed out a second example, namely, that there exist animalcule ferments of the genus Vibrio which can live without free oxygen, was only a particular incident appertaining to a mode of fermentation which is perhaps the most wide-spread in nature.

"The conditions under which putrefaction is manifested may vary considerably. Suppose, in the first instance, the case of a liquid, that is to say of a putrescible substance, of which all the parts have been exposed to contact with the air. Either this liquid may be shut up in a close vessel, or it may be placed in an open vessel, having an aperture more or less large. examine in succession what happens in the two cases.

I will

"It is commonly known that putrefaction takes a certain time to manifest itself, and that this time varies according to temperature, neutrality, acidity, or alkalinity of the liquid. Under the most favourable circumstances a minimum of about twenty-four hours is necessary before the phenomenon begins to be manifested by external signs. During this first period the liquid is agitated by an internal movement, the effect of which is to deprive of its oxygen the air which is in solution, and to replace it by carbonic acid gas. The total disappearance of the oxygen when the liquid is neutral or slightly alkaline is due, in general, to the development of the smallest of the infusoria, the Monas crepusculum and Bacterium termo. A very slight agitation occurs as these little beings travel in all directions. When this first action of exhausting the oxygen in solution is accomplished, they perish and fall to the bottom of the vessel like a precipitate; and if by chance the liquid contains no fecund germs of the ferments I have spoken of, it remains indefinitely in this condition without putrefactionwithout fermenting in any way. This is rare, but I have met with several examples. Most frequently when the oxygen in solution has disappeared, the vibrion ferments, which have no need of this gas, begin to appear, and putrefaction immediately sets in. Gradually it accelerates itself, following the progressive march of the development of the vibrions. The putridity

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becomes so intense that the microscopic examination of a single drop is very unpleasant. The fetid odour depends chiefly on the proportion of sulphur the substance contains. The odour is scarcely sensible if the matter is not sulphuretted, as, for example, in the fermentation of the albumenoid matter which water can carry away from the yeast of beer. The same is the case with butyric fermentation; and after my experiments butyric fermentation must, from the nature of its ferment, be considered as a phenomenon of exactly the same order as putrefaction properly so called. Thus we see what happens when putrefaction is in some sort restrained."

"It results from what precedes, that contact with air is not necessary to the development of putrefaction, but that, on the contrary, if the oxygen, dissolved in a putrescible liquid, is not removed by the action of special beings, putrefaction will not occur, as the oxygen would cause the vibrions to perish if they tried to develope themselves."

"I shall now examine the case of free putrefaction in contact with air. That which I have already said might make it appear that it could not take place under such circumstances, as oxygen kills the vibrions which excite it. Notwithstanding this, I shall demonstrate that putrefaction in contact with air is more complete than when it is effected under shelter from air."

"Let us go back to our aerated liquid, this time exposed to contact with air in a wide-mouthed vessel. The removal of the oxygen takes place as previously described. The difference is that the bacteriums, etc., do not perish, but propagate themselves to infinitude at the surface of the liquid which is in contact with the air. They form a thin pellicle, which gradually thickens, falls into rags to the bottom of the vessel, is formed again, and so forth. This pellicle, with which is usually associated divers mucors and mucedines, prevents the solution of oxygen gas in the liquid; and thus permits the development of the vibrio-ferments. For them the vessel is as if closed against the introduction of air. They can even multiply in the pellicle at the surface, because they find themselves protected by the bacteriums and mucors against too direct an action of the atmospheric air."

"The putrescible liquid thus becomes the seat of two kinds. of action, very distinct, and which are in relation to the physiological functions of the two kinds of beings that nourish themselves in it. The vibrions, on one hand, living without the aid of atmospheric oxygen, determine, in the interior of the liquid, acts of fermentation-that is to say, they transform nitrogenous substances into more simple, though still complex, products. The bacteriums or the mucors burn these same products, and

bring them back to the simple condition of binary compounds, water, ammonia, and carbonic acid."

"We have yet to distinguish the very remarkable case in which the putrescible liquid forms a layer of slight thickness with easy access to atmospheric air. I shall demonstrate experimentally that both putrefaction and fermentation may be absolutely prevented, and that the organic matter will yield only to the operation of combustion."

"Such are the results of putrefaction effected with free contact with the atmosphere. On the contrary, in the case of putrefaction under shelter from the air, the products of the doubling of the putrescible matter remain unchanged. This is what I meant when I said that putrefaction in contact with air is a phenomenon, if not always more rapid, at least more complete, more destructive of organic matter, than putrefaction under shelter from air. In order to be better understood I shall cite some examples. Let us putrefy-I employ the word designedly in this instance as a synonym of ferment-let us putrefy lactate of lime sheltered from air. The vibrion-ferments will transform the lactate into several products, one of which is always butyrate of lime. This new compound, indecomposable by the vibrio which provoked its formation, will remain indefinitely in the liquid without any change. But repeat the operation in contact with air. As fast as the vibrion-ferments act in the interior of the liquid, the pellicle on the surface gradually and completely burns the butyrate. If the fermentation is very active this combustion is arrested, but entirely because the carbonic acid that is disengaged hinders the arrival of atmospheric air. The phenomenon recommences as soon as the fermentation is finished or lessened in rapidity. It is precisely the same if we cause a naturally sweet liquid to ferment under shelter from air, the liquid is charged with alcohol almost indestructible; while if we operate with contact of air, the alcohol after being acetified is burnt and transformed entirely into water and carbonic acid. Then the vibrions appear, and in their suite putrefaction, when the liquid only contains water and nitrogenous matter. At length in their turn the vibrions and the products of putrefaction are burnt by the bacteriums or the mucors, of which the last survivors incite the combustion of their predecessors, and thus is accomplished the return of the organized matter to the atmosphere and to the mineral kingdom."

"Let us now consider the putrefaction of solid bodies. I have recently shown that the body of an animal is, under

"De doublement de la matière putrescible." Pasteur means the products of the putrefactive fermentation, which he has described as complex, though more simple than the original substances.

ordinary circumstances, shut against the introduction of the germs of inferior beings; consequently putrefaction begins first at the surface, and afterwards reaches the interior of a solid mass. If a whole animal is left after death either in contact with, or sheltered from, air, its surface is covered with germs of inferior organism which the atmosphere has conveyed. Its intestinal canal in which fecal matters are formed is filled not only with germs, but with fully developed vibrions, as Leewenhoek perceived. These vibrions are much in advance of those on the surface of the body. They are adult individuals, deprived of air, bathed in liquids, and in process of multiplication and function-performance. It is by their aid the putrefaction of the body begins, which has only been preserved up to that time by life and the nutrition of its organs.'

After a few observations M. Pasteur declares his conviction that "neither in their origin nor in their nature is there any resemblance between putrefaction and gangrene," and he adds, "instead of being a putrefaction properly so called, gangrene appears to be that condition of an organ in which one part is preserved in spite of death from putrefaction, and in which the liquids and solids act and react chemically and physically beyond the normal actions of nutrition."

We shall only remark upon this very important and interesting paper that few English microscopists adhere to Ehrenberg's notion, which is adopted by M. Pasteur, that vibrions are animals. On the contrary, Drs. Arlidge, Williamson, Burnett, and other authorities, agree with Cohn that they belong to the vegetable kingdom, and are in many cases transitional forms of Algæ.