42 BACTERIOLOGY. 



there exists a specific group of bacteria, the nitrifying 

 bacteria, that seem to 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 growth 

 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 kills 

 them. Certain species and developmental forms, on 

 the contrary, though incapable of multiplying when in 

 the dry state, may be completely deprived of their water 

 without causing them to lose the power of reproduction 

 when again placed under favorable conditions. 



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, 

 as well as in the end products of such nutrition, for 

 instance: one species may require a tolerably concen- 

 trated form of nutrition, while another needs but a very 



