478 Journal of Agricultural Research voi. v. no. n 



As to the activity of soil protozoa, Cunningham (i, p. 56) states: 



To the question as to whether the protozoa lead an active life in the soil, it has been 

 showTi that the action of heat combined with the dilution method does not give a 

 definite answer. That question, however, is answered in the affirmative by the re- 

 sults of experiments which will now be discussed. 



Martin and Lewin (8, p. 117) likewise in a recent article concluded 

 that " it seems probable from the vi^ork that we have done up to the pres- 

 ent that there are always some free living protozoa present in a trophic 

 state in even relatively dry, poor soils. " 



In this study it is the purpose of the writer — 



(i) To develop a method for studying protozoan activity in the soil. 



(2) To ascertain whether the protozoa lead an active life in soils of 

 different moisture content when the temperature is constant and when 

 it is variable. 



(3) To study the effect of moisture on the activity of the protozoa in 

 the soil under constant and variable temperatures. 



(4) To study the length of the period of excystment of soil protozoa. 



METHOD FOR STUDYING PROTOZOAN ACTIVITY IN THE SOIL 



In studying the activity of protozoa in the soil the first difficulty which 

 is encountered is the lack of a suitable method by which the investigator 

 can determine with certainty the extent to which these organisms are 

 active in the soil. Several methods are recorded that have been used 

 with more or less success. In 191 1 Goodey (2) passed an electric current 

 through the medium and found that the living protozoa traveled with 

 the current to the cathode. The separation of active forms by centrif- 

 ugation was attempted by Russell and Golding (10) in 191 2. In 191 3 

 Martin (6) discussed a simple method based on the mixing of a small 

 quantity of soil with picric acid and then noting the organisms (bacteria, 

 protozoa, and diatoms) which rose to the surface, when this mixture 

 was placed in a wide dish and the soil stirred. Cunningham (i) em- 

 ployed the dilution method for examining and counting the protozoa in 

 the soil. Martin and Lewin (8) discuss several methods which they 

 have employed with more or less success. For the detection of living 

 amebae, an air-blast method which they have devised has proved to be 

 the most successful. 



It was suggested by Martin and Lewin (8, p. no) that — 



Any method which depends upon the addition of water to the soil must admit of 

 very rapid execution, otherwise there is danger of protective cysts present in the soil 

 opening, and thus giving a false impression as to the constitution of the active fauna. 

 This danger is probably a very real one in the case of small flagellates, and especially 

 the resting forms of some green algse, in the case of which a few minutes' immersion in 

 water may make the difference between a resting and an active form. 



