so it can be shown with equal clearness and certainty that the entire
process of what is known as putrescence is equally and as absolutely
dependent on the vital processes of a given and discoverable series of
organisms.

Now it is quite customary to treat the fermentative agency in
putrefaction as if it were wholly bacterial, and, indeed, the
putrefactive group of bacteria are now known as saprophytes, or
saprophytic bacteria, as distinct from morphologically similar, but
physiologically dissimilar, forms known as parasitic or pathogenic
bacteria.

It is indeed usually and justly admitted that _B. termo_ is the
exciting cause of fermentative putrefaction. Cohn has in fact
contended that it is the distinctive ferment of all putrefactions, and
that it is to decomposing proteinaceous solutions what _Torula
cerevisiæ_ is to the fermenting fluids containing sugar.

In a sense, this is no doubt strictly true: it is impossible to find a
decomposing proteinaceous solution, at any stage, without finding this
form in vast abundance.

But it is well to remember that in nature putrefactive ferments must
go on to an extent rarely imitated or followed in the laboratory. As a
rule, the pabulum in which the saprophytic organisms are provided and
"cultured" is infusions, or extracts of meat carefully filtered, and,
if vegetable matter is used, extracts of fruit, treated with equal
care, and if needful neutralized, are used in a similar way. To these
may be added all the forms of gelatine, employed in films, masses and
so forth.