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. 



\ 



Fig. 57. Lactic ferment in a Fig. 58. Lactic ferment 



cbciplet (^ciiut/.e..berger). (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 Bacterium (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. 



