tJY K. ailKlG-SMlTil. 66 i 



oi' protozoa that had l)eeii destroyed, luive been proportional to 

 the bacteria that were killed; and that, so tar as numbers are con- 

 cerned, the Hiatus quu remained after the treatment with disin- 

 fectants? I 



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

 granules, Goodey* concludes that the Colpoda tirst to appear in 

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

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

 terial activity in soils. 



As the ciliates, such as Colpuda tuvitllua, 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 i)hagocytosis as with the limitation of tlie 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 influence of the excreted 

 products of the digested bacillary protoplasm, f On the other 

 hand, it is possible that substances of the 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 amtrba; 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 suspension of amoeba?. Amoeba Umax, from a 



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

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

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

 inovint; in plant-infusions, and in no case have I seen tiie undoubted in- 

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

 aside the living hacleria. atid pass over the dead microbes [a trace of 

 methylene blue added to the drop under examination colours the dead 

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

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

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

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

 seconds, swim awaj-. 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 



