440 



Observations on Soil Protozoa 



in Part I of this paper. Immediately before examination the fluid was 

 subjected to the action of osmic vapour for a few seconds to kill the 

 ciliates. 



* F indicates that the suspension was filtered through the solid material. 



Experiments in which the strength of suspension, time of action, 

 and amount of solid matter used were varied demonstrated that the 

 different kinds of materials per gram were capable of retaining specific 

 numbers of organisms per c.c. (see Table VI). P'or the sake of convenience 

 the numbers below are given to the nearest thousand. 



Coar.se Sand 



27,000 



Fine Sand 

 185.000 



Soil 

 280,000 



Ignited Soil 



270,000 



Clay 

 450,000 



These figures are much lower than those obtained with experiments 

 on amoebae and flagellates, as was expected on account of the enormously 

 greater size of the ciliate. 



The ratio which one substance bears to another as regards capacity 



