454 Mr. T. Goodey. Investigations on Protozoa in 



151 days the bacterial content of the inoculated soil remained at a lower level 

 than that of the toluened soil. At the same time it appears to be pretty 



.200 

 E '80 



•-a wo 



ai q.100 

 in 80 

 c fin 



2| 40 



2 zo 



TOLUENED 



32 60 93 125 151 173 208 259 301 337 350 386 454 487 



□ AYS. 



Fig. 8. 



clear that the two curves are of the same order. The T. + 5 per cent, 

 untreated does not show a continuous and persistent decline in the numbers 

 of bacteria, as one would expect if the limiting factor were due to the growth 

 and activity of protozoa added with the untreated soil. The two curves are 

 practically parallel from 259 clays onwards, and it is obvious that the same 

 set of conditions was affecting the bacteria in each soil. 



The numbers of protozoa present in each soil are as follows : — In the 

 T. + 5 per cent, untreated there are at least 10,000 flagellates, about 

 500 amoebae, and an almost negligible number of ciliates — 5 or 10 — per 

 gramme.* In the toluened soil there are about 5000 flagellates and about 

 10 amoebae per gramme. There are thus very many more protozoa per 

 gramme in the inoculated soil than in the toluened soil, and the lower 

 bacterial content of the former soil is thus easily accounted for if we assume 

 that the protozoa act as the limiting factor. If we only had these two 

 curves and that for the untreated soil on which to base our conclusions, the 

 above inference might be considered correct. But when we take into con- 

 sideration the points already mentioned in connection with the other 

 inoculated soils, it is scarcely possible to assume that this is the real 

 explanation. 



It has been shown that in the case of the toluened and the T. + Bacteria 

 soils that the flagellates can be left out of account, so far as any possibility of 

 functioning as the limiting factor is concerned. So that if the lower bacterial 



* This soil affords evidence of the activity of the amoebae added in the 5 per cent, of 

 untreated soil. Amoebae are present in the latter to the extent of about 3000 per gramme, 

 and assuming that this number was present at the time the soils were mixed, we can 

 reckon that in each 100 grm. of the mixture there were 15,000 amoebae or 150 per gramme. 

 There were present at the last protozoal count 500 per gramme, thus showing that the 

 original 150 had increased to 500 per gramme. Similarly the 1846 + 10 per cent. 1870 

 soil discussed on p. 447 gives evidence of the amcebas added in the 10 per cent, of 1870 soil 

 having increased from 50 per gramme at the beginning to 2000 per gramme at the end 

 of the experiment. 



