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T. L. HILLS 



sion of normal soil known to contain protozoa. The remaining 

 half were inoculated with the same amount of soil free from 

 protozoa. The protozoa-free soil was obtained by sterilizing a 

 portion of the Miami soil and inoculating it with as many kinds of 

 bacteria as could be isolated by the plate method, using differ- 

 ent kinds of media. The flasks were then incubated at room 

 temperature (approximately 22° to 25°C) and the ammonia and 

 nitrate content determined at the end of four, eight and twelve 

 weeks. The ammonia was determined by distilling 100 grams 

 of the soil with 10 grams of magnesium oxide and 250 cc, distilled 

 water. The distillate was received into N/20 sulphuric acid 

 and the excess acid remaining after the distillation was titrated 

 with alkali of the same normality. The nitrate was determined 

 by the phenolsulphonic acid method. 



The results of this work are given in the following table: 



TABLE 1 

 Ammonia and nitrate in soils with and without protozoa 



From the data of table 1 it will be noted that in the soil contain- 

 ing protozoa the ammonia decreased somewhat while in the 

 soil free from protozoa it tended to increase to a slight extent. 

 This may be explained by the fact that in the soil containing 

 protozoa the nitrifying organisms were also present and func- 

 tioning, whereas in the soil free from protozoa they were absent 

 and thus the ammonia tended to accumulate. In the case of 

 the nitrate formation, in the soil with protozoa the nitrate con- 



