STUDIES ON SOIL PROTOZOA 



171 



the development of the two classes of micro-organisms subse- 

 quent to treatment with volatile antiseptics runs parallel. 

 This experiment was verified by another test in which normal 

 and carbon bisulphide-treated soils were compared. In this 

 test (Table XXXI) the number of bacteria in the treated soil 

 rose above that of the control soil by the fifteenth day, but at 

 this period the protozoa in the treated soil had also returned 

 to their normal level. It is seen also that the number of bacteria 

 continued to increase after the protozoa had again become as 

 numerous as in untreated soil. 



TABLE XXXI 

 Effect of CSi Upon the bacteria and protozoa in soil 



The reinoculation of partially sterilized soils 



In their work at the Rothamsted Station Russell and Hutchin- 

 son (1913) claim to have demonstrated that the soil contains a 

 detrimental factor since the bacterial content of partially steril- 

 ized soil may be reduced by reinoculation with untreated soil. 

 It is pointed out that when soil treated with a volatile antiseptic 

 is reinoculated with 5 per cent of untreated soil the number of 

 bacteria is reduced, while if only 0.5 per cent of normal soil is 

 added no such reduction takes place. These observations are 

 explained by the assumption that when onlj'- 0.5 per cent of 

 untreated soil is added the harmful factor is not transmitted, 

 but when 5 per cent is used for the inoculum the treated soil 

 again becomes infected with the undesirable group of organisms. 

 The soundness of this view may certainly be questioned, as 

 it is difficult to understand why it should be necessary to use 

 such a large amount of untreated soil in order to insure the pres- 

 ence of a factor which is supposed to exist in amount sufficient 

 to suppress the bacteria. A review of the work of Russell 



