organism, nor, judging by the standard of our present knowledge, of one specified class of vegetative forms, but by organisms which, though related to each other, are in many respects greatly dissimilar, not only morphologically, but also embryologically, and even physiologically.

Moreover, although this is a matter that will want most thorough and efficient inquiry and research to understand properly its conditions, yet it is sufficiently manifest that these organisms succeed each other in a curious and even remarkable manner. Each does a part in the work of fermentative destruction; each aids in splitting up into lower and lower compounds the elements of which the masses of degrading tissue are composed; while, apparently, each set in turn does by vital action, coupled with excretion, (1) take up the substances necessary for its own growth and multiplication; (2) carry on the fermentative process; and (3) so change the immediate pabulum as to give rise to conditions suitable for its immediate successor. Now the point of special interest is that there is an apparent adaptation in the form, functions, mode of multiplication, and order of succession in these fermentative organisms, deserving study and fraught with instruction.

Let it be remembered that the aim of nature in this fermentative action is not the partial splitting of certain organic compounds, and their reconstruction in simpler conditions, but the ultimate setting free, by saprophytic action, of the elements locked up in great masses of organic tissue—the sending back into nature of the only material of which future organic structures are to be composed.

I have said that there can be no question whatever that Bacterium termo is the pioneer of saprophytes. Exclude B. termo (and therefore with it all its congeners), and you can obtain no putrefaction. But wherever, in ordinary circumstances, a decomposable organic mass, say the body of a fish, or a considerable mass of the flesh of a terrestrial animal, is exposed in water at a temperature of 60° to 65° F., B. termo rapidly appears, and increases with a simply astounding rapidity. It clothes the tissues like a skin, and diffuses itself throughout the fluid.

The exact chemical changes it thus effects are not at present clearly known; but the fermentative action is manifestly concurrent with its multiplication. It finds its pabulum in the mass it ferments by its vegetative processes. But it also produces a visible change in the enveloping fluid, and noxious gases continuously are thrown off.

In the course of a week or more, dependent on the period of the year, there is, not inevitably, but as a rule, a rapid accession of spiral forms, such as Spirillum volutans, S. undula, and similar forms, often accompanied by Bacterium lineola; and the whole interspersed still with inconceivable multitudes of B. termo.

These invest the rotting tissues liked an elastic garment, but are always in a state of movement. These, again, manifestly further the destructive ferment, and bring about a softness and flaccidity in the decomposing tissues, while they without doubt, at the same time, have, by their vital activity and possible secretions, affected the condition of the changing organic mass. There can be, so far as my observations go, no certainty as to when, after this, another form of organism will present itself; nor, when it does, which of a limited series it will be. But, in a majority of observed cases, a loosening of the living investment of bacterial forms takes place, and simultaneously with this, the access of one or two forms of my putrefactive monads. They were among the first we worked at; and have been, by means of recent lenses, among the last revised. Mr. S. Kent named them Cercomonas typica and Monas dallingeri respectively. They are both simple oval forms, but the former has a flagellum at both ends of the longer axis of the body, while the latter has a single flagellum in front.

The principal difference is in their mode of multiplication by fission. The former is in every way like a bacterium in its mode of self-division. It divides, acquiring for each half a flagellum in division, and then, in its highest vigor, in about four minutes, each half divides again.

The second form does not divide into two, but into many, and thus although the whole process is slower, develops with greater rapidity. But both ultimately multiply—that is, commence new generations—by the equivalent of a sexual process.

These would average about four times the size of Bacterium termo; and when once they gain a place on and about the putrefying tissues, their relatively powerful and incessant action, their enormous multitude, and the manner in which they glide over, under, and beside each other, as they invest the fermenting mass, is worthy of close study. It has been the life history of these organisms, and not their relations as ferment, that has specially occupied my fullest attention; but it would be in a high degree interesting if we could discover, or determine, what besides the vegetative or organic processes of nutrition are being effected by one, or both, of these organisms on the fast yielding mass. Still more would it be of interest to discover what, if any, changes were wrought in the pabulum, or fluid generally. For after some extended observations I have found that it is only after one or other or both, of these organisms have performed their part in the destructive ferment, that subsequent and extremely interesting changes arise.

It is true that in some three or four instances of this saprophytic destruction of organic tissues, I have observed that, after the strong bacterial investment, there has arisen, not the two forms just named, nor either of them, but one or other of the striking forms now called Tetramitus rostratus and Polytoma uvella; but this has been in relatively few instances. The rule is that Cercomonas typica or its congener precedes other forms, that not only succeed them in promoting and carrying to a still further point the putrescence of the fermenting substance, but appear to be aided in the accomplishment of this by mechanical means.

By this time the mass of tissue has ceased to cohere. The mass has largely disintegrated, and there appears among the countless bacterial and monad forms some one, and sometimes even three forms, that while they at first swim and gyrate, and glide about the decomposing matter, which is now much less closely invested by Cercomonas typica, or those organisms that may have acted in its place, they also resort to an entirely new mode of movement.

One of these forms is Heteromita rostrata, which, it will be remembered, in addition to a front flagellum, has also a long fiber or flagellum-like appendage that gracefully trails as it swims. At certain periods of its life they anchor themselves in countless billions all over the fermenting tissues, and as I have described in the life history of this form, they coil their anchored fiber, as does a vorticellan, bringing the body to the level of the point of anchorage, then shoot out the body with lightning-like rapidity, and bring it down like a hammer on some point of the decomposition. It rests here for a second or two, and repeats the process; and this is taking place by what seems almost like rhythmic movement all over the rotting tissue. The results are scarcely visible in the mass. But if a group of these organisms be watched, attached to a small particle of the fermenting tissue, it will be seen to gradually diminish, and at length to disappear.

Now, there are at least two other similar forms, one of which, Heteromita uncinata, is similar in action, and the other of which, Dallingeria drysdali, is much more powerful, being possessed of a double anchor, and springing down upon the decadent mass with relatively far greater power.

Now, it is under the action of these last forms that in a period varying