VII.] 



THE PROTOZOA OF THE SOIL 



233 



evaporated. The moisture in the soil was then adjusted, 

 whereupon the soil showed the same increase in its 

 crop-producing power. The effects were most pronounced 

 with initially rich soils, and the plants grown in the 

 treated soil showed every evidence, in their vigour of 

 growth and the colour of the leaves, of an increased 

 supply of nitrogen. Analysis showed an increased 

 content in nitrogen, and, to a much smaller extent, of 

 phosphoric acid and potash, but the whole effects were 

 similar to those produced by a more liberal nitrogenous 

 manuring. 



On examination of the soils, it was found that the 

 treatment, either by heat or antiseptics, had not effected 

 the sterilisation of the soil. Some groups of bacteria 

 were destroyed, e.g., the nitrification organisms ; but 

 the decay organisms and those producing ammonia 

 were still present. Moreover, and this is the significant 

 fact, a count of the number of bacteria present in the 

 soil showed invariably that, though the first effect of 

 the treatment was to depress the numbers present, they 

 very rapidly increased, until they reached numbers 

 vastly greater than were ever found in the untreated 

 soil. The following table illustrates the point : 



Bacteria in Millions per Gram of Dry Soil. 



