150 Bacteria in Relation to Country Life 



The soils that allow a rapid disappearance of their 

 humus are usually sandy or sandy loams, warm and 

 well drained. The air circulates freely in them down to a 

 considerable depth; the soil bacteria, particularly the 

 aerobic species, develop in great numbers, and the carbon 

 of the humus is returned to the air as carbon dioxid. 

 Decay, under such conditions, is really slow burning, 

 and the organic matter is, in time, reduced to a little 

 heap of ash, as if it had been destroyed by fire. The 

 term " eremakausis, " which means slow burning, has 

 been applied to this process. 



It has been demonstrated by analyses of air contained 

 in the soil that its oxygen is used up rapidly in this 

 bacterial burning of the humus. Such soil-air has been 

 found to contain as much as 9 per cent of carbon dioxid 

 and only about 11 per .cqnt of oxygen, instead of the 

 20.90 per cent of oxygen and .03 to .04 per cent of carbon 

 dioxid found, on the average, in the air above the soil. 

 The average of nineteen analyses of soil-air, made by 

 von Fodor, showed 2.54 per cent of carbon dioxid and 

 18.33 per cent of oxygen; whereas, the air above the 

 soil contained .04 per cent of carbon dioxid and 20.96 

 per cent of oxygen. 



All this goes to show that not only is the carbon in 

 the humus changed to carbon dioxid, but that this is 

 accomplished at the expense of the oxygen in the soil- 

 air. When the oxygen is thus used up rapidly, the de- 

 composition of the humus is checked somewhat, and it 

 is conceivable that soil-air deprived of all, or nearly all, 

 of its oxygen will no longer supply the proper condi- 

 tions for decay. It happens, however, that in the open 



