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.