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VITAL MA XIFES TA TIONS OF BA CTERIA . 2 7 .

Malate of lime also undergoes several kinds of fermentation,
forming propionic, butyric, acetic, and lactic acids.
Tartrate of lime yields propionic or butyric acid, and, accord-
ing to Fitz, alcohol, acetic, and traces of succinic acids.
Finally, citrate of lime yields acetic acid, with ethyl alcohol
and succinic acid as by-products. (See Fliigge, Micro-organisms,
p. 489.)
In accordance with the various fermentative processes specified
in the foregoing pages, a particle of starch introduced into the oral
cavity would undergo about the following successive changes : In
the first place it is, in part at least, transformed into grape-sugar
by the diastase of the saliva (ptyaline). This, in turn, is split into
lactic acid through the action of various bacteria in the mouth.
The lactic acid unites with the lime of the teeth, or tartar, form-
ing lactate of lime. The latter, according to the investigations
of Fitz and others just referred to, may then undergo various
fermentations, giving rise to new acid products and to the for-
mation of the corresponding lime-salts, from which, by still other
processes of fermentation, acids are again derived. The process,
however, most probably ceases after the formation of lactate of
lime.
D. Putrefaction.
AYben the decomposition of a culture medium is accompanied
by the development of stinking, for the most part gaseous pro-
ducts, ammonia, sulphuretted hydrogen (NII3, SH^), etc., the
process is commonly designated as putrefaction. AibuaiijiQUS
substances are especially liable to putrefaction ; also the albu-
minoids (glue-giving substances), peptones, and lastly, some sub-
stances related to the albuminous bodies,—leucine, tyrosine,
indol, etc.
It is evident, however, that this definition by no means involves
a precise chemical or bacterio-chemical process, and that the
presence or absence of stinking gases cannot be made an absolute
criterion by which to judge of the real nature of the changes
going on in a medium containing bacteria.
The appearance of putrefactive products in any fermentation
does not depend alone upon the kind of fermentation and the