42 BACTERIOLOGY. 



there exists a specific group of bacteria, the nitrifying 

 bacteria, that apparently increase and multiply without 

 appropriating proteid nutrition. They are concerned 

 in the particular form of fermentation that results in 

 the oxidation of ammonia to nitrous and nitric acids, a 

 process everywhere in progress in the superficial layers 

 of the soil. 



For the supply of carbon many of the carbon com- 

 pounds serve as sources upon which the bacteria can 

 draw. The carbon deficit, for example, can be obtained 

 from sugar and bodies of like composition ; from glyc- 

 erin and many of the fatty acids ; and from the alka- 

 line salts of tartaric, citric, malic, lactic, and acetic 

 acids. In some instances carbon compounds, which 

 when present in concentrated form inhibit the growtli 

 of bacteria, may, when highly diluted, serve as nutri- 

 tion for them. Salicylic acid and ethyl alcohol are of 

 this class. 



In addition to carbon and nitrogen, water is essential 

 to the life and development of bacteria. Without it 

 no development occurs, and in many cases drying the 

 organisms results in their death. Certain species and 

 developmental forms, on the contrary, though incapable 

 of multiplying when in the dry state, may be com- 

 pletely deprived of their water without causing them 

 to lose the power of reproduction under favorable con- 

 ditions. 



Closer study of bacteria, and a more intimate ac- 

 quaintance with their nutritive changes, demonstrate 

 an appreciable variability in the character of the sub- 

 stances best suited for the nutrition of different species, 

 one requiring a tolerably concentrated form of nutri- 

 tion, while another needs but a very limited amount 



