STUDIES ON SOIL PROTOZOA 55 



and then reinoculated, one set without protozoa and the other 

 set with protozoa. The moisture content was held at 8 per cent 

 and samples were taken for bacterial analysis at the end of 30, 

 45 and 60 days. The results are given in Table X. These show 

 that the relation between the number of bacteria in the presence 

 and absence of protozoa is the same in soils of low water content 

 as when more moisture is present. This fact argues strongly 

 against the protozoan theory. 



The development of bacteria in soils containing protozoa and free of 



protozoa 



As is well known, protozoa do not multiply as rapidly as 

 bacteria. It is also the contention of Russell and Hutchinson 

 that the biological factor, which they beUeve to exist in soils, 

 requires much more time to develop in soil than is necessary for 

 the bacterial flora. If such a factor exists in the soil there should 

 be a difference in the development of bacteria in soils containing 

 protozoa and soils free of protozoa. We should expect the bacteria 

 to multiply very rapidly in each soil and to attain about the same 

 maximum numbers. At a later period, in soil containing protozoa, 

 the number of bacteria should diminish very appreciably, due to 

 the development of the ''detrimental factor," while the number 

 of bacteria in the protozoa-free soil should remain much nearer 

 its maximum. It has been observed on a number of occasions 

 that the difference in the number of bacteria which develop in 

 the soils inoculated with normal soil and Avith protozoa-free 

 soil is apparent fifteen days after inoculation, and also that the 

 difference in the two flora apparently remains the same from 

 the fifteenth day through the third month. (Tables V, VI, VII 

 and VIII.) The harmful factor, if such exists, must develop 

 within fifteen days after the soil is inoculated. 



Two pots of a rich garden soil, two of a field soil (loam) and 

 two of a poor sandy soil were steriHzed. One pot of each was 

 then inoculated with normal soil and the other pot from each 

 set inoculated with protozoa-free soil. Bacterial counts were 

 made every day for sixteen days. The data obtained are tabu- 

 lated in Table XI. 



