170 



Mr. T. Goodey. A Contribution to our [May 19, 



Activity on the surface of the soil must not, however, be confused with 

 activity in it. 



Part II. — Experimental. 

 Perhaps the most important point to determine is the state in which the 

 protozoa are present in the soil. We know they are there, but to exercise 

 the function which has been attributed to them by Kussell and Hutchinson 

 they must be present in a free-living, active condition, capable of a certain 

 amount of movement consequent upon their need for food, moisture and 

 oxygen. 



On account of the opacity and texture of the soil, it presents insuperable 

 difficulties in the way of direct microscopic observation of such minute 

 organisms as protozoa. Even when finely teased out in a liquid and spread 

 in a thin layer in a glass trough, it has never been possible to find free-living 

 organisms. 



Further, the method employed for cultivating them described above does 

 not throw any light upon their condition. There is nothing to tell us 

 whether the forms which occur in the culture have developed from a free- 

 living or from an encysted condition. 



For the elucidation of this question various experiments have been carried 

 out, both " indirect," i.e. designed to give certain data on which inferences 

 could be based as to the condition of the protozoa, and " direct," i.e. designed 

 to affect the activities of any free-living protozoa in the soil and induce them 

 to leave it. 



In the following pages an account is given, first, of the direct attempts, and 

 second, of an indirect method which has proved very useful. 



(d) Thermotaxis. — A piece of apparatus was constructed on the same 

 principles as that described by Jennings.* It consisted of three glass 

 tubes about 8 mm. in diameter, supported in a horizontal position at exactly 

 the same level, by being passed through holes in a block of wood. The tubes 

 were placed 1 inch apart and so arranged that a glass slide rested evenly on 

 each, giving complete contact of the surfaces. Indiarubber tubes were 

 connected to the ends of the glass tubes and attached, on the inflow side, to 

 water taps, one supplying water at about 15° C. and the other leading from a 

 geyser, by means of which water at any required temperature from 15 to 60° C. 

 could be obtained. The waste water was led off by rubber tubes emptying 

 into a sink. 



A glass trough was made by cementing strips of glass to a slide 3 inches 

 by 1*5 inch with Canada balsam ; the trough was about 6-5 cm. long, To cm. 



* H. S. Jennings, ' The Behavior of Lower Organisms,' Carnegie Institution, 

 Washington, 1904, No. 16, p. 11. 



