BY R. GREIG-SMITH. 173 



substances, as for example, Bac. pyocyaneus, and moulds may be 

 capable of doing the same. But these are not the only inhabit- 

 ants of the soil. There are certain protozoa, and with the failure 

 to obtain a decided and undoubted production from the bacteria 

 and moulds, the attention was turned to the soil-fauna. 



With regard to the possible activity of the members of the 

 soil-fauna in this direction, we are faced with the fact, that the 

 introduction of certain species of protozoa, e.g., the Amoebse and 

 Colpodse into sterile soils, does not bring about the condition that 

 holds before sterilisation. The bacterial numbers, which become 

 greatly increased as a result of the sterilisation, do not become 

 reduced to the previous level when the protozoa are present. 

 It is true that Goodey* has lately shown that the inhibiting 

 factor, which determines the reduction of the bacterial numbers, 

 becomes evident when the numbers of amoebae approach and 

 exceed 50,000 per gram of dry soil, but, at the same time, he 

 says that the sterilised or disinfected soils are not suitable media 

 for the production of the factor. The treatment of the soil with 

 heat or with the volatile disinfectants so alters the soil, that it is 

 not immediately suitable for developing the inhibiting factor, 

 whatever it may be. 



I had considered the possibility of soil-amceba? being able to 

 produce substances akin to the immune bodies of the animal 

 pathologist, but, as experimental work failed to reveal any sign 

 of toxic substances, and such immune bodies must be included 

 in this category, I simply record the fact that such a possibility 

 had been entertained, and that experiments with, and without, 

 "vaccines" had been negative. 



Some difficulty was met with in obtaining a "pure" culture of 

 soil-amoebse. Upon a former occasion, they had been cultivated 

 in quantity in 1% liay-infusion, without any trouble, but, upon 

 repeating the procedure, it was found that the medium was not 

 well adapted for the purpose. The single cells generally disap- 

 peared overnight. The trouble was traced to the medium being 

 too nutritive, thus permitting the accompanying bacteria to 

 become too numerous and render the medium too alkaline. A 



* Proc. Roy. Soc, 89 (B.616), p.297. 



