114 THE STORY OF GERM LIFE. 



beginning. Under these conditions the lack of 

 moisture and air prevents fermentative action 

 very largely. Only certain acid-producing organ- 

 isms grow, and these very slowly. The essential 

 result in either case is that the common putrefac- 

 tive bacteria are prevented from growing, proba- 

 bly by lack of sufficient oxygen and moisture, 

 and thus the decay is prevented. The closely 

 packed food offers just the same unfavourable 

 condition for the growth of common putrefactive 

 bacteria that we have already seen offered by the 

 hard-pressed cheese, and the bacteria growth is 

 in the same way held in check. Our knowledge 

 of the matter is as yet very slight, but we do 

 know enough to understand that the successful 

 management of a silo is dependent upon the 

 manipulation of bacteria. 



THE FERTILITY OF THE SOIL. 



The farmer's sole duty is to extract food 

 from the soil. This he does either directly by 

 raising crops, or indirectly by raising animals 

 which feed upon the products of the soil. In 

 either case the fertility of the soil is the funda- 

 mental factor in his success. This fertility is a 

 gift to him from the bacteria. 



Even in the first formation of soil he is in a 

 measure dependent upon bacteria. Soil, as is well 

 known, is produced in large part by the crum- 

 bling of the rocks into powder. This crumbling 

 we generally call weathering, and regard it as due 

 to the effect of moisture and -cold upon the rocks, 

 together with the oxidizing action of the air. 

 Doubtless this is true, and the weathering action 

 is largely a physical and chemical one. Never- 



