STUDIES ON SOIL PROTOZOA 



49 



flora of this soil is limited by some harmful factor. In all of the 

 tests which have been made the soils free of protozoa contained 

 greater numbers of bacteria than the corresponding soils which were 

 inoculated with normal soil. The results obtained in a few repre- 

 sentative trials are given in Table V. 



TABLE V 



The number of bacteria in soils free of protozoa and containing protozoa 



Test 1* — Incubation period two months 



Test 2 — Incubation period one month 



340,000,000 

 275,000,000 



307,500,000 



106,000,000 

 114,000,000 



110,000,000 



Test 3 — Incubation period three months 



230,000,000 

 180,000,000 



205,000,000 



142,000,000 

 140,000,000 



141,000,000 



* Each of these tests represents a distinct experiment and not a re-count on 

 the same soil. 



An experiment was also performed to see if the above phe- 

 nomena would occur on different tyipes of soil. For this pur- 

 pose a rich muck soil, a clay loam and a poor sandy soil were 

 used. The results obtained (Table VI) showed the characteristic 

 difference in each case. 



The results obtained in the foregoing experiments can not be 

 considered as proof that the soil protozoa are inimical to the 

 bacteria because of the differences in the two soils under con- 

 sideration. However, these data, together with the previous 

 observations that the soil contains an adequate supply of protozoa 

 and that some of these organisms are active, certainly appear to 

 add weight to the theory of Russell and Hutchinson that protozoa 

 serve as a hmiting factor upon the bacteria in the soil. 



