84:2 CONTRIBUTIONS TO OUR KNOWLEDGE OP SOIL-FERTILITY, xii., 



soils. 'J'he volatile disinfectant favoured the development of an 

 active, though restricted, fauna, and a flora consisting largely of 

 slime-forming bacteria. The control-tests had a very diverse 

 flora and fauna, while the toluened tests grew a very numerous 

 crop, consisting almost entirely of colpodae, amoebae, and small 

 monads, and the suspensions were covered with a thick, gela- 

 tinous film of bacteria. In Giltay's solution, the controls were 

 always of a paler colour than the treated tests. The flora had 

 undoubtedly suffered a considerable diminution in its species, 

 and the idea appeared feasible, that, possibly, the reason for the 

 non-appearance of the protozoa in the toluened moist soils, might 

 be due to the absence of certain bacteria, killed off by the 

 toluene. 



In order to test the matter, a raw garden-soil was shaken up 

 in Giltay's solution, and the supernatant liquid was centrifu- 

 galised. Minute drops were taken, and examined microscopi- 

 cally for protozoa. Those free from all suspicion of protozoa, 

 were taken up in capillary tubes and dropped into Giltay's solu- 

 tion. The growth consisted of bacteria only. Drops of this 

 subculture were introduced into tubes containing Giltay's solu- 

 tion and portions of treated soil. Examination of these, from 

 time to time, showed that they were no better, so far as the 

 growth of protozoa was concerned, than tests without the addi- 

 tion of the bacteria. The idea that the bacteria might have an 

 influence upon the development of the fauna in treated soils, 

 therefore, was not substantiated. 



In one medium, namely, dilute dextrose nitrate bouillon, an 

 observation was made, which appeared to explain the inability of 

 ciliates to grow in the tests made with the all a vial soil. Other 

 media containing easily reducible organic matter, such as hay- 

 infusion, showed the same phenomenon. The soil is of a pale 

 smoke-colour, and it was noted that the medium remained 

 normal, when ciliates were present, but, in their absence, a dark- 

 coloured, filmy growth formed in the dilute bouillon. This 

 settled on the sedimented soil, the upper layers of which were 

 distinctly black. The dark-coloured film consisted of bacteria 

 and soil-particles, containing black fragments, which became 



