BY K. GltKIG-SMlTM. 661 



ul protozoa that bad been destroyed, bave been proportional to 

 tbe bacteria that were killed ; and tliat, so far as numbers are con- 

 cerned, the status quo remained after the treatment with disin- 

 fectants ? 



From the appearance of the protoplasm and the absence of food- 

 granules, Goodey* concludes that tbe Colpoda first to appear in 

 soil-cultures, have emerged from tbe encysted condition, and that 

 they, therefore, do not functionate as a factor in limiting the bac- 

 terial activity in soils. 



As tbe ciliates, such as Culpuda ciicullus, cannot be credited with 

 the limitation of the soil-bacteria, we must examine the claims of 

 the amoebae; and be it remembered, that we are not so much con- 

 cerned with phagocytosis as witii the limitation of tbe bacteria. 



Even if the amoebae do actively ingest bacteria, in the soil, there 

 is no evidence that the net result may not be an increase of the 

 residual microbes from the stimulating intiuence of the excreted 

 products of the digested bacillary protoplasm.! On the other 

 band, it is possible that substances of tlie nature of immune bodies 

 may be secreted or excreted by the amoebae. The matter clearly 

 cannot be decided ex cathedra, and, accordingly, an experiment 

 was begun, in which a number of amoebae were added to a soil that 

 had been freed from protozoa by heating at 65° and treatment 

 with chloroform. Subsecjuent tests showed that the soil was free 

 from protozoa. A susjiension of amoebae. Amoeba Umax, from a 



* Proc. Roy. Soc. B.84, 18/8/11, p. 179. 

 t The amcebas undoubtedly are phagocytes, but they certainly do not 

 englobe every microbe they chance to meet, for I have watched soil-amcebae 

 moving in plant-infusions, and in no case have I seen the undonbteil in- 

 gesting of a bacterium. I iiave seen the protruding pseudopodia push 

 aside the living bacteria, and pass over the dead microbes [a trace of 

 methylene blue added to the drop under examination colours the dead 

 cells but not the living] which can be traced under the amtuba as it glides 

 along, and which are left upon the spots thej' originally occupied. A 

 motile bacterium may touch the protozoon, and dart off again, or it may 

 be caught, presumably by the flagelia, and after wriggling about for some 

 seconds, swim awa}-. Again, a protruding pseudopodium may touch a 

 bacterium and immediately retract, or a distinct angular bay may be 

 formed as the pseudopodium meets and passes the microbe. Rotating 



