FERMENTS, ENZYMES, TOXINS AND PTOMAINS 51 



tiply without appropriating proteid nutrition. They are, as 

 stated above, concerned in the particular form of fermenta- 

 tion that results in the oxidation of ammonia to nitrous and 

 nitric acids, a process everywhere in progress in the super- 

 ficial layers of the soil. 



For the supply of carbon many of the carbon compounds 

 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 glycerin and many of the 

 fatty acids; and from the alkaline 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 nutrition 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 dried without causing them to lose the power of 

 reproduction when again placed under favorable conditions. 



Closer study of bacteria, and a more intimate acquain- 

 tance with their nutritive changes, demonstrate an appre- 

 ciable variability in the character of the substances 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 concentrated form of nutrition, 

 while another needs but a very limited amount of proteid 

 substance for its development; some bring about profound 

 alterations in the media in which they are growing, while 

 others produce but little apparent change; for certain species 



