312 



Dr. T. Goodey. Further Observations on 



3. The residual protozoa of a treated soil fail to increase in numbers, even 

 though the conditions are favourable to great bacterial activity. 2 and 3 

 show that the treated soil alone is an unsuitable medium for active trophic 

 existence of protozoa. 



Another point calls for some comment. Russell has claimed,* on the 

 strength of Martin and Lewin's results.f that the culture fauna is distinct 

 from the trophic fauna of a soil, and has criticised the results in my previous 

 communication by suggesting that there is nothing to show that in the 

 introduction of mass protozoa cultures the real trophic fauna was reintro- 

 duced into the soil. I agree that the criticism is probably justified. At the 

 same time, however, I would suggest that too much emphasis should not be 

 laid on the distinction between the trophic and the culture fauna, for the 

 results which I have recorded from the (T + 5 per cent. U) and (H + 5 per 

 cent. U) soils show that at least two or three species of amoeba?, viz., 

 Amoeba Umax, Amoeba terricola, and Gephyr amoeba delicatula, are capable of 

 leading an active existence and of multiplying in the soil, and must therefore 

 have constituted the trophic fauna, or an important part of it, during the 

 course of the experiment. These are all forms which occur readily in 

 culture ; in fact, it is by the agar-plate method that I have been able to 

 demonstrate their presence and active multiplication in the soil. 



A word also is perhaps necessary here on the numerical estimation of 

 soil protozoa, especially in view of the remarks of Martin and Lewin on this 

 subject in their last joint paper.J The results given for the (T + 5 per 

 cent. U) and the (H + 5 per cent. U) soils show that the agar-plate and the 

 hay-infusion methods are practicable for giving rough approximations of the 

 numbers of soil protozoa. The methods as employed in this piece of research 

 are probably more reliable than the dilution method, in which soil is shaken 

 up with a liquid followed by the transference of measured quantities of the 

 soil suspension to nutrient media, for I have inoculated both agar -plates and 

 hay-infusion with actual weighed quantities of soil, from 1 grin, down to 

 O0002 grm., and hence have eliminated certain of the experimental errors 

 incident to the nse of the dilution method, which has only been used for 

 obtaining quantities of soil smaller than - 0002 grm. 



As methods they undoubtedly leave much to be desired, for there are so 

 many uncontrollable factors entailed in their use. At the same time they 

 are the only methods at present available, and one is justified, I think, in 



* 'Roy. Soc. Proc.,' B, vol. 89, p. 82 (1915). 



t 1 Phil. Trans.,' vol. 205, pp. 79-94 (1914) ; and ' Journ. Agric. Sci.,' vol. 7, pp. 106-119 

 (1915). 



% 'Journ. Agric. Sci.,' vol. 7, p. 109 (1915). 



