BY R. GREIG-SMITH. 175 



number of amoebse were added to each droplet, and a trace of 

 chalk. All the cultures did well, and, in course of time, the 

 mobile forms encysted. The cells of the urea-test were vegetat- 

 ing long after the others, and the amoebse in the ammonium 

 chloride test also persisted longer, and finally disappeared with- 

 out forming cysts. 



A preliminary experiment was made with an extract of a 

 partially exhausted leaf-mould, using a growth of amoebae derived 

 from a single cell. Although the solutions were tested from 

 time to time in the customary manner for the influence of boiling 

 and dilution, no definite information was obtained, and it was 

 concluded that the culture-solution was too poor in nutrients to 

 show or develop any signs of toxicity. 



Vegetable-mould neutralised with lime (p. 168) was then used. 

 Each test contained the equivalent of ten grams of dry organic 

 matter with an amount of water sufficient to cause the soil to 

 adhere loosely to the sides of the containing bottle. This meant 

 73% of moisture. It was apparent from the results that the 

 mould became too acid for the continued growth of the amoebae. 

 Forty thousand were added to each bottle, and, in five days, they 

 had increased to 1*6 millions, in twelve days they had decreased 

 to 136,000 mobile forms, and, by the twentieth day, they all had 

 encysted. While this was going on, the extract, originally 

 neutral, became more and more acid, doubtless due to the carbon 

 dioxide, produced by the activity of the bacteria introduced with 

 the amoebae, reacting with the calcium humate, and liberating 

 free humic acid. 



The test was repeated with similar results. On the sixth day, 

 the amoebae had increased forty-four fold, and the reaction of the 

 extract was - 0-04 ; on the thirteenth day, the amoebae had 

 encysted, and the reaction was -i-O-l. The bacterial numbers 

 gave no information. 



Better results were obtained with an infusion of hay made b}^ 

 diluting a 1% infusion with tap-water to make a 0-2% solution. 

 Tests were made on the sixth, twentieth, and forty-second days, 

 but, as the two latter gave somewhat normal dilution-curves, 

 they are not recorded. 



