148 Bacteria in Relation to Country Life 



place in the absence of bacteria and of other microorgan- 

 isms. The bacteria are thus the great scavengers of 

 the living world, supplementing the work of the green 

 plants. These are the builders of organic materials, 

 the bacteria are the tireless destroyers. Under their 



attack the roots 



j>\ I* and the stubble of 



I 9 it ^M V f cultivated crops, 

 V 2 ^ ^ the leaves and twigs 



j m J of forest trees, or 



J f * the bulk of barn- 



9 w + S 



J yard and green-ma- 



/f ^ \^ nures are changed 



y\^ f* $*^~ slowly into dark- 



^ / 7^ J* *$ colored humus sub- 

 Fig. 22. Cellulose ferments, causing the breaking Stances. Without 

 down of woody tissue. 1,2, and 3. Hydrogen > > ,-, 

 bacillus; X 2,000. (Omelianski.) 4, 5 and bacteria and Other 

 6. Methane bacillus; X 2,000. ( Om elian 9 ki., micro6rganisms 



such changes would not take place at all, or else very 

 slowly. 



It has been demonstrated time and again that soils 

 sterilized by heat, or treated with antiseptic substances, 

 like chloroform, carbon bisulfid, or carbolic acid, either 

 cease to give off carbon dioxid, or yield only minute 

 quantities of it. Similar soils, not sterilized, continue 

 to form large amounts of this gas. Furthermore, soils 

 or quantities of manure that have been sterilized begin 

 to give off carbon dioxid in large quantity soon after 

 they are inoculated either with pure cultures of certain 

 bacteria, or with mixtures of several species. It has 

 thus been established that the decomposition of vege- 



