THE VITAL PHENOMENA OF BACTERIA. 129 



tion of alcohol and butyric acid from glycerin ; 

 the viscous fermentation of sugar with forma- 

 tion of gum or mannite ; the dextrine fermen- 

 tation of carbohydrates ; the viscous fermenta- 

 tion of proteids ; the blue and red coloration of 

 milk (the latter may be due to different causes) ; 

 the formation of blue cheese ; the fluorescence 

 and phosphorescence shown in some culture 

 media ; the production of ammonia and sul- 

 phuretted hydrogen ; and the formation of 

 nitric and acetic acids. 



As regards the occurrence and distribution of 

 bacteria, it may be said in general that these 

 organisms are to be found almost everywhere. 

 They are present in the soil, in the water and 

 in the air. Differences in distribution, however, 

 do occur. In the upper layers of the soil are 

 found not only enormous numbers but many 

 different kinds of germs favored by the fluctua- 

 tions in humidity and by the varying temper- 

 ature. Here in the ground they take part in 

 the decomposition of organic substances, and 

 convert these to ammonia, oxidize the ammonia 

 to nitric acid, and form carbonic acid ; indeed, 

 we may look upon bacteria as the most impor- 

 tant promoters of the decompositions called 

 putrefaction and decay. The ground, how- 

 ever, acts upon bacteria like a filter, so that the 

 number quickly diminishes from above down- 



