446 



Mr. T. Goodey. Investigations on Protozoa in 



This is good evidence, I think, that the protozoa have not functioned as the 

 limiting factor. 



In the case of the soils inoculated with cultures of amoebae and flagellates 

 obtained from 1870 soil, the curves for the bacterial counts of which are 

 shown in fig. 3, the general inference to be drawn is that after a period of 



32 63 82 124 153 181 232 284 324 360 363 419 486 519 



DAYS. 



Fia. 3. 



18 months in which to act, the protozoa have not exerted a limiting action 

 on the bacteria in their respective soils. 



At 519 days the bacterial content of both inoculated soils is well above 

 that of the untreated soil. 



The amoebae in the sample of soil specially inoculated with them are present 

 to the extent of 10,000 per gramme, whilst in the flagellate-inoculated soil 

 there are 10,000 flagellates and about 2000 amoebae per gramme. These 

 results are very interesting, for they indicate that even when protozoa are 

 present in the soil in such large numbers and under conditions favourable to 

 active existence they do not exert a depressing effect on the bacteria. 



The amoeba curve is especially significant, for it shows that even in the 

 presence of 10,000 amoebae per gramme of soil the bacteria can maintain 

 a higher level in numbers than in the original soil containing no protozoa. 



The curve for the flagellate-inoculated soil does not call for much comment. 

 It is practically identical with that for the untreated soil during a great 

 part of its length, but on the whole is at a higher level and indicates that the 

 10,000 flagellates and 2000 amoebae per gramme are not capable of bringing 

 the bacterial content down below the level of the untreated soil. 



Fig. 4 shows the curves for the untreated soil and for the sample to which 

 10 per cent, of 1870 soil was added. At the end of 519 days the untreated 

 soil is at a lower level than the U. + 1870, though from 232 days onwards 

 the two curves are very similar, and from 360 days to the end of the 

 experiment may be considered as identical. There are about 2000 amcebse and 

 2000 flagellates per gramme in the mixed soil, and the curves show that these 

 have not been able to bring down the bacteria to a level below that of the 



