298 



Dr. T. Goodey. Further Observations on 



Methods. 



The soil used was a fibrous loam obtained from stacked turf. It was 

 friable, and worked easily, containing about 18 per cent, of water by weight. 

 Lots of 400 grm. were put up in quart bottles previously sterilised and 

 plugged with cotton-wool. In order to partially sterilise the soil it was 

 treated with 2 per cent, of toluene, which was allowed to act for two days, 

 after which the soil was spread out in order to allow the antiseptic to evaporate. 

 By inoculating some of the soil treated in this way on to nutrient agar, it 

 was found that amoebae and flagellates developed after a few days' incuba- 

 tion. The soil was therefore heated in a steamer regulated at 65° C. for 

 2 hours, in the hope of killing off all the remaining protozoa. At the end of 

 this treatment bacterial counts by the gelatine plate method were made, and 

 the moisture content of the soil determined. More agar plates were 

 inoculated with small quantities of the soil to test for the presence of 

 protozoa, and after about 10 days' incubation a few amoebae and flagellates 

 were found on the surface of the medium, thus showing that the heating 

 had not eliminated all the protozoa. However, no further attempt was made 

 to eradicate these remaining forms except in the case referred to on p. 301, 

 and the inoculation of the desired protozoa into the soil samples was proceeded 

 with. 



In order to obtain a large number of protozoa free from bacteria I devised the 

 following method, which, in brief, consisted in driving by means of an electric 

 current free-swimming ciliates and other protozoan forms from a medium in 

 which bacteria abounded into a similar medium free from bacteria. For this 

 purpose a glass trough supported in a wooden frame was constructed. It 

 measured about 7 inches in length by 4 inches in width, and was divided 

 transversely into two equal parts by an upright glass partition which did 

 not quite reach to the height of the two sides, and thus allowed of free 

 communication between the two halves over the top of it. The trough, 

 supported on the stand of a dissecting microscope, is shown in fig. 1. In 

 using the apparatus I proceeded as follows. A mixed culture of ciliated 

 protozoa from soil was made in 1-per-cent. hay -infusion, the following 

 organisms being present : — Colpoda cncullus, Col. maupasii, Col. steinii, 

 G-onostomum ajtne, Urostyla sp., besides a large number of amoebae and 

 flagellates. The surface layers of the culture containing a vast number of 

 organisms were skimmed off and put on one side, whilst the bulk of the 

 culture was filtered through a sterile Berkfeld filter so as to free it from 

 bacteria. The mixed culture of protozoa and bacteria was poured into one 

 side of the trough to the requisite height and into the other half was poured 



