8 MODERN DAIRY PRACTICE. 



consider the bacteria producing fermentations. For this 

 reason the following short account of the conditions of 

 life of bacteria holds good primarily in case of this 

 group. 



Nutrition of Bacteria. The bacteria are usually ex- 

 ceedingly unpretentious in their demands for the good 

 things of life, a fact which, of course, is one of the main 

 reasons for their universal distribution in nature. The 

 smallest quantities of organic matter are sufficient for 

 their support ; and wherever they find such a substance 

 which possesses the moisture and heat necessary for their 

 development and a reaction favorable to their activity, 

 they will grow and multiply there. 



The bacteria live on the ready-formed carbonaceous 

 compounds of organic origin, and do not as a rule possess 

 the ability to make use of carbonic acid. The different 

 species of bacteria usually select different kinds of carbo- 

 hydrates. Some thrive best when the nutritive solution 

 contains grape-sugar ; others when it contains cane-sugar 

 or milk-sugar, etc. Hence we find that the different 

 nutritive substances often are contaminated with their 

 own peculiar kinds of bacteria. Only a few bacteria are 

 omnivorous and satisfied with almost any organic sub- 

 stratum. 



The nitrogen in the nutritive substratum required by 

 the bacteria may be obtained not only from organic sub- 

 stances, but from certain inorganic materials, like nitric acid 

 and ammonia compounds. The bacteria, however, usually 

 prefer albuminoids. Very few bacteria can do entirely 

 without nitrogeneous substances. The need of the dif- 

 ferent species of nitrogen varies greatly. The bacteria 

 living mainly on carbohydrates need only very minute 



