106 MICROBES, FERMENTS, AND MOULDS. 
fermentation, after which it turns sour and produces 
lactic acid and mannite, 
Lactic fermentation requires the presence of pro- 
teid matters in process of decomposition, and it can 
only be carried on when the degree of acidity in the 
liquid does not exceed definite limits. For this purpose 
a certain amount of chalk is added, to neutralize the 
acid formed at the expense of the sugar. 
It is somewhat difficult to observe the microbe of 
this fermentation without previous instruction. It 
appears in the form of grey patches, which are readily 
confounded with casein, and with the disintegrated 
gluten, or the chalk of the liquid under examination. 
S, = Je 
18 fo ab 
as 
Fig. 57.—Lactic ferment in a Fig. 58.—Lactic ferment 
chaplet (Schutzenberger). (Pasteur). 
Under the microscope the patch is seen to consist of 
minute globules, or of filaments with very short articu- 
lations, isolated or in flakes. These are the characters 
of the genus Bacteriwm (Figs. 57, 58). The globules 
are much more minute than those of the yeast of beer, 
and are strongly agitated when in isolation by a 
motion incorrectly termed Brownian movement, and 
which does not in reality differ from the movements 
which may be observed in most of the spores of the 
lower orders of plants, and in a great number of 
bacteria. 
