Andrew C'rNxiNGHAM 



y.) 



{h) Effect of Moisture. 



(i) On the number of protozoa hi soils. In the following experiments 

 the temperature was kept constant at 22° C. 



Experiment I. The water content of a sample of garden soil 

 was adjusted to 70 % of its water-holding capacity and a determination 

 of the number of protozoa present was made by means of the dilution 

 method. The sample was divided into three portions. In the first 

 case 10 grams of the soil was placed in a petri dish. The lid was kept 

 raised so as to allow of evaporation of moisture but prevent contamina- 

 tion from the air. The second portion consisted of 30 grams of soil, 

 also in a petri dish. This sample was saturated with water and the 

 lid allowed to remain in position to prevent evaporation as much as 

 possible. The third portion consisted of the remainder of the sample 

 in a flowerpot covered with cotton-wool to minimise evaporation but 

 allowing free access of air. The first portion was allowed to dry for nine 

 days, the second was kept saturated for eight days, while the third 

 was kept at 70 % w.h.c. for seven days. At the end of these periods 

 a determination of protozoa was made for each portion. In the case 

 of the dry and saturated samples quantities corresponding to one gram 

 of the 70 % sample were taken for the dilutions. The results are 

 shown in Table 8. 



Table 8. 



The efEect of drying is seen in the reduction of the total numbers. 

 The 70 % and saturated samples have given the same increase. The 



