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 deg. to 65 deg.  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.