32 Bacteria in Relation to Country Life 



injured or suppressed by comparatively slight amounts 

 of sugar, and the failure of putrefying organisms to 

 develop in milk under ordinary conditions is ascribed 

 directly or indirectly to the influence of the milk-sugar. 

 The range of carbon compounds used by bacteria as a 

 source of food is very large. Grape-sugar, cane-sugar, 

 milk-sugar, malt-sugar, and mannite, a compound 

 closely related to the sugars, are readily used by many 

 organisms, as are also such compounds as starch, dex- 

 trin and cellulose, capable of being changed into sugar. 



The compounds of carbon in bacteria. — The energy 

 stored up in these substances is employed for the manu- 

 facture of the compounds found in the bacterial body. 

 In other words, the bacteria burn up the sugars and 

 allied materials in a manner analogous to the burning 

 up of the food in the animal body. 



The carbon compounds enumerated consist of three 

 chemical elements — carbon, hydrogen, and oxygen. 

 There are, however, still other classes of carbon com- 

 pounds seized upon with even greater avidity by im- 

 portant groups of bacteria. The compounds in question 

 are the proteins — composed of carbon, nitrogen, hydro- 

 gen, oxygen, and sulfur, — and substances derived from 

 the proteins and composed of carbon, nitrogen, hydro- 

 gen and oxygen. The numerous species of decay- and 

 putrefaction -bacteria are especially favored in their 

 development by protein compounds and grow rapidly 

 in meat and meat extracts, egg-albumin, and other 

 materials of animal or vegetable origin, rich in protein. 

 For this reason, beef-broth, supplemented by mineral 

 salts, is used almost universally in bacteriological labora- 



