310 Dr. T. Goodey. Further Observations on 



at the beginning of the experiment showed approximately 30,000 amoebae 

 per gramme, whilst those made towards the end of the experiment show 

 the same number per gramme, thus indicating that there has been no 

 activity and multiplication of the organisms added. For this reason I do 

 not interpret the fall in the curve of the bacterial numbers in (T + A) as due 

 to the action of amoebae. How then is the sharp rise and the subsequent 

 drop in the curve to be accounted for ? The only explanation I can furnish, 

 and I think that it meets the situation, is that the nutrient agar on which 

 the amoebae had been growing, and of which small quantities were unavoid- 

 ably added along with the encysted amoebae, supplied a suitable extra food 

 substance for the bacteria of the soil, and that they multiplied on this, and 

 when it was exhausted their numbers fell again. It thus comes into line 

 with the soils inoculated with hay -infusion, where the extra food supplied 

 gave rise to an enormous increase in bacterial numbers. 



The 30,000 amoebae per gramme were added in an encysted condition, and 

 there is no evidence that they ever excysted and became active, probably for 

 the same reason that the protozoa in the other treated and inoculated soils 

 failed to become active and to multiply, i.e., because of the unsuitability of 

 the treated soil as a medium for active trophic existence. 



Discussion. 



The failure of the inoculated protozoa in the (T -I- C) and (T + M) soils and 

 of the residual protozoa in the (T + F) soil to multiply, except in the one case 

 of the Amceba Umax in (T + C), is interesting, and is probably open to the 

 same explanation as that advanced above for the similar phenomena in the 

 (T + "W) and (T + A) soils, viz., the treated soil, for some obscure reason, 

 does not afford a suitable medium for protozoal activity. This of itself is 

 probably a sufficient explanation, but two other points are worthy of con- 

 sideration in the case of these soils. ' Very high numbers of bacteria were 

 present early in the experiment, and these may have tended to check 

 protozoal activity, for Cunningham* has shown that the presence of large 

 numbers of bacteria checks the development of protozoa in a medium. It is 

 also possible where a soil receives a mass inoculation of protozoa sufficient to 

 give large numbers of protozoa per gramme that this in itself may tend to 

 inhibit their further increase in numbers. 



A comparison of the curves from the mass inoculation experiments of the 

 present and the previous investigation reveals a remarkable similarity in 



* ' Journ. Agric. Sci.,' vol. 7, Part I (1915). 



