4U 



fore projected and continued for 28 days — from February 9th to 

 March 8th. During the last 14 days the bacteria also were 

 counted. The following- conclusions were drawn : — 



I. — There is a daily variation in the number of trophic forms 

 of the three species of Haj^ellates, Oicomonas sp. (Martin) , 

 Cercomonas longicmida and Bodo sp., in the soil of arable fields. 



2. — The numbers of bacteria and trophic anujeba; in the soil are 

 correlated, varyinj>- inversely over a period of 14 days. 



3. — Temperature and rainfall apjDear to have no intluence on 

 the number of active protozoa in the soil. 



(Note. — In view of the importance of these results counts 

 were begun on July 4th. 1920, and have gone on daily ever since: 

 it is j^roposed to continue these for 365 {^onserutive davs.) 



XVII. D. \W. Cutler. " Obseyvatioiis on Soil Protozoa." 

 Journal of Agricultural Science, 1919. Vol. IX. 

 pp. 430-444. 



It is shown that soil possesses a remarkable power o( retaining 

 j3rotozoa. When a suspension of protozoa is shaken with soil all 

 the organisms are withdrawn until the saturation point is reached, 

 after which, for the first time, the supernatant liquid contains pro- 

 tozoa. Some of the results are : — 



Active flagellates and amoebcp. 

 millions per c.c. of suspension. 



Before shaking with soil 



After ,, „ ,, • ; • 



Number taken up per gram of soil 



Until the soil has absorbed 1.7 millions per gram there is com- 

 plete retention of the organisms. 



One gram of coarse sand is capable of withdrawing approxi- 

 mately 145,000 amoibse and flagellates from a suspension of any 

 strength. Fine sand withdraws approximately 980,000 : soil and 

 partially sterilised soil 1,650,000, ignited soil 1,500,000, and clay 

 2,450,000 per gram of material in each case. 



. These figures are constant for given material and organisms, 

 and are independent of the concentration of the suspensions, the 

 time of action, or whether the suspension contains cysts or active 

 forms of the amcebaj and flagellates investigated. Also the actioti 

 is the same when the experiment is performed with a suspension of 

 living or dead organisms. 



Experiments with the ciliate — Colpoda cucullus — show that 

 coarse sand retains 27,000; fine sand 185,000; soil and partially 

 sterilised soil 270,000 and clay 450,000 per gram of material. 



The importance of this work arises from the fact that some of 

 the previous investigators have examined soil suspensions under 

 the microscope for protozoa, and have drawn certain conclusions 

 from failure to find active forms. The present investigation shows 

 that the method is unreliable and the conclusions, therefore, not 



I 



