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no THE MICRO-ORGANISMS OF THE HUMAN MOUTH.

The result was the same, and need not be given ; the two an-
alyses above described being abundantly sufficient to show that
the acid generated by the fiingus in question is the common fer-
ment lactic acid. Distillate No. 1, referred to above, owed its
slight acidity, we now know, in pai't at least to lactic acid, since,
when an aqueous solution of lactic acid is boiled, a small fraction
of the acid goes over with the water. To ascertain, however,
whether any other acid, especially volatile, was present, the dis-
tillate was boiled witli carl)onate of lime, tiltercd, evaporated to
dryness, a small amount of dilute sulphuric acid added, and
heated in a retort over the water-bath ; a few drops of an oily
acid came over, which, when taken upon the lingers, smelled like
butyric acid ; the amount, however, was so small that no attempt
could be made to analyze it.
Among the i^roducts of fermentation of these bacteria I have
also found formic,* acetic, and butyric acids, the latter, however,
only in very small quantities. The greatest amount of acid which
I have as yet observed in lactic acid fermentation is 0.75 per
cent. Although the coefficient of separation of lactic acid is very
small compared to that of the inorganic acids, it is, nevertheless,
rather large when compared to that of other organic acids. My
investigations have convinced me that it is consideral)ly increased
in syrupy solutions, so that instead of 10, the coefficient for
aqueous solutions, a niulti}»le of 10 must be taken, large quanti-
ties of ether (one and a half to two liters) being necessary to
effect even an approximate extraction of the acids.

Formation of Gas in Ladir Acid Fcrnicntation.
The fermentations which are brought al)ont by diiferent lactic
acid bacteria show great ditferences in respect to the amount of
gas evolved. I have already called attention to the fact that the
fermentations of carbohydrates frequently proceed without gen-
erating the least trace of gas. On the other hand, some of the
bacteria more recently examined formed ver^- large quantities of
gas (CO2 and H), so that the gelatine in the culture-tubes was
* The distillation with phosphoric acid was made verj' carefully over the water-
bath.