What Bacteria Do 23 



preserve its individual character under all the 

 varying conditions and vicissitudes to which 

 it is subject. They are to be found every- 

 where in nature. Where putrefaction and de- 

 cay are going on they are most abundant, but 

 where any form of life can exist they are pres- 

 ent, either dry and inactive, or where moisture 

 and food are present, growing and multiplying 

 in such degree as their surroundings will per- 

 mit. In all natural surface waters, in the soil, 

 on all fruits, vegetables, and plants; in the 

 nose, mouth, digestive canal, and excreta 

 of men and animals; on the skin, wherever 

 dust can go or collect, there are bacteria of 

 various forms in greater or smaller numbers. 

 They are the scavengers in the economy of 

 nature. 



The great bacterial laboratory of the earth 

 is the soil. Here the most wonderful things 

 happen under the friendly influence of these 

 tiny germs. With the aid of other lowly liv- 

 ing things, they help in the gradual erosion 

 of the rocks, from which the mineral ingre- 

 dients of the soil arise. They pull the tissues 

 of dead trees and plants and animals asunder, 



