178 Agricultural Bacteriology. 



thing teeming with forms of life of the greatest import- 

 ance to the farmer. It is a manufacturing establish- 

 ment where plant food is made from raw materials. To 

 furnish the workers favorable conditions is one of the 

 problems the successful tiller of the soil must solve. 



Decomposition of organic matter. The material re- 

 turned to the soil under natural conditions or by the 

 farmer in the form of stable manure or the crops plowed 

 under (green manuring) is organic in character, i. e., 

 the result of plant and animal growth. It contains the 

 elements that are necessary for succeeding crops of vege- 

 tation, but in such a form that they cannot be used until 

 they have again been brought to the same condition as 

 when they were first taken up by the plant. 



The organic matter added to the soil embraces every 

 conceivable type of matter, yet, everything serves as a 

 food for some form of life, and is thus decomposed to 

 some extent. Other kinds of life then use the by-prod- 

 ucts of the first and so on until the ultimate stage is 

 reached and the elements can be again made use of by a 

 new crop of wheat, corn, or other plant. The spoiling of 

 our food stuffs, rotting of apples, and potatoes, the sour- 

 ing of milk, the putrefaction of meat, and the rotting of 

 manure, are but steps in this great series of decomposi- 

 tion processes carried on largely by bacteria. 



The digestive changes occurring in all kinds of ani- 

 mals are but initial steps in the decomposition of organic 

 matter, since the material given off from their bodies is 

 much more simple than the food absorbed and is much 

 more easily brought, by the action of bacteria, into a 

 form that can be used by the green plant. 



The various kinds of matter added to the soil can be 

 divided into three classes: 1st. The carbohydrates; 2nd. 



