32 SA GTEBIOL OGY. 



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 the 

 organisms results in their death. Certain forms, on 

 the contrary, though incapable of multiplying when in 

 the dry stage, may be completely deprived of their 

 water without causing them to lose the power of repro- 

 duction when favorable conditions reappear. 



The closer study of the bacteria, and a more intimate 

 acquaintance 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 

 of proteid substance for its development. Certain 

 members bring about most profound alterations in the 

 media in which they exist, while others produce but 

 little apparent change. In one case alterations in the 

 reaction of the media will be conspicuous, while in 

 another no such variation can be detected. With the 

 growth of some forms products resulting from specific 

 processes of fermentation appear. Other varieties pro- 

 duce poisons of remarkable degrees of toxicity, while 

 the growth of otlicrs may be accompanied by the bodies 

 characteristic of putrefaction. 



For the normal development of bacteria it is not only 

 essential that the sources from whi(!h they can obtain 

 the necessary nutritive elements should exist, but ac- 



