432 Ohservations on Soil Protozoa 



the hollow, and covered by the cover-glass. The preparation is then 

 examined under the microscope, the magnification generally being 

 approximately 600 diameters. 



The protozoa in each square are then counted. Estimates are made 

 from five samples of each solution and the results averaged. The motility 

 of the organism is usually insufficient to cause trouble ; but if it does, the 

 fluid is first exposed to osmic acid vapour, which kills the protozoa very 

 rapidly. Kopeloff, Lint and Coleman also suggest a method by which 

 the organisms may be stained and killed in one process, but this I find 

 unnecessary. 



Table I. 



Method used for counting in a suspension Protozoa whose number per c.c. 



is greater than 100,000. 



Method used for counting in a suspension Protozoa whose number per c.c. 



is less than 100,000. 



Sample 



Average number per c.c. of suspension, 4400. 



Two methods were employed for calculating the results. 



1. The number of protozoa in ten squares is counted and the average 



for one square found. As one square is 0-04 sq. mm. and the depth 0- 1 mm. 



the cubical volume is 0-004 cu. mm. The number of protozoa per cubic 



centimetre of the suspension is found by multiplying the average count 



, 1000 „^. „.„ 

 per square by rr?j^ =^ z50,000. 



