304 



Dr. T. Goodey. Further Observations on 



beginning of the experiment there has been an increase in the numbers of" 

 this organism from about 600 to 30,000 per gramme, whilst for Amoeba 

 terricola and Gephyramoiba delicatula there has been a multiplication from a 

 few per gramme to about 200 per gramme of each species. 



The flagellates also show evidence of marked activity, having increased from 

 1500 to 10,000 per gramme. The two species of ciliates have also increased' 

 considerably in numbers. This multiplication of protozoa has gone hand in 

 hand with the depression in the bacterial numbers at 43 days and the only- 

 conclusion, I think, that can be drawn from this is that the bacterial decrease- 

 in numbers is the direct effect of the protozoal increase in numbers. This result 

 definitely supports the hypothesis of Eussell and Hutchinson and constitutes 

 the first record of its kind in the course of the investigations on this problem.. 

 The results of the protozoal counts seem to suggest that the chief part in the 

 depressing action of the protozoa on the bacterial numbers at 43 days must 

 be ascribed to the Amoeba Umax, which attained the high figure of 30,000 per 

 gramme. It is interesting to note also that the later count at the 210th day- 

 shows no increase in the number of Amoeba Umax over the 30,000 per 

 gramme reached at 43 days, whereas the Amoeba terricola and Gephyramoeba 

 delicatula have each increased from 200 to 1000 per gramme. 



From this it would appear possible that a particular soil may only be capable 

 of supporting a certain maximal number of one species of amoeba, which in the- 

 case of this soil is about 30,000 per gramme of the Amoeba Umax in question. 

 This is, however, merely a tentative suggestion. 



The Table shows that the Toluenecl plus sterile distilled water soil (T + W)? 

 ha'd initially about 100 Amoeba Umax and 1000 flagellates per gramme, whilst 

 counts made at 320 days showed about 200 Amoeba Umax, and no flagellates,, 

 the latter failing to appear in the cultures. This indicates that there has 

 been practically no activity and multiplication on the part of the amoeba in. 

 this soil. In the (T + 5 per cent. U) soil, however, there has been marked 

 activity and multiplication of the protozoa, and from this it would appear that 

 a treated soil does not afford a suitable medium for protozoal activity and that 

 in order to render it suitable a small quantity of untreated soil must be 

 added to it. 



2. Confirmatory Experiment. 



In view of the important character of the results just described, another 

 experiment was started in order if possible to obtain confirmation of them. 

 A quantity of soil from the same source as that used in the earlier experiment 

 was taken and partially sterilised by heat. For this purpose 800 grm. were- 

 taken and put up in thin test-tubes and then put into a steamer regulated at 

 72° C. and left there for five hours in the hope of killing off all forms of protozoa. 



