Sept. IS, 1915 



Soil Protozoa 



515 



Table IV. — Experimental error when all the organisms of the loop numbering about 

 140,000 per cubic centimeter are counted under the low power of the microscope 



Probable error = ±0.6745 



V 16, 672 



672-3 



= 13.62. 



= ±0.6745X13.62 = 9.20. 

 Percentage of error = 9.20-^285.0 = 3.23. 



Table V. — Probable error when the organisms of several fields are counted and when the 

 number totals about 4^0,000 per cubic centimeter 



Probable error =±0. 6745-./ ^' ^^^' ^ 

 V 90 



= 4- 15- 



= ±0. 6745 X 4- 15 = 2. 799- 

 Percentage of error = 2. 799-5-36. 6= 7. 64. 



The average of the experimental error incurred in counting is therefore 

 5.87 per cent. 



