32 BACTERIOLOGY. 



them. Salicylic acid and ethyl alcohol come under this 

 head. 



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 reproduction 

 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 mem- 

 bers 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 reac- 

 tion of the media will be conspicuous, while in another 

 no such variation can be detected. With the growth 

 of some forms products resulting from processes of 

 fermentation appear. Other varieties produce poisons 

 of remarkable degrees of toxicity, while the growth of 

 others may be accompanied by the bodies characteristic 

 of putrefaction. 



For the normal development of bacteria it is not only 

 essential that the sources from which they can obtain 

 the necessary nutritive elements should exist, but account 

 must also be taken of the products of growth of the 

 organisms in these substances. Nitrogen and carbon 

 compounds in the proper form to be taken up and 



