SOIL PROTOZOA* 



By George P. Koch, 

 Research Fellow, the New Jersey College for the Benefit of Agriculture and Mechanic Arts 



I.— METHOD FOR COUNTING PROTOZOA 



INTRODUCTION 



Repeated claims that soil protozoa are detrimental to other soil micro- 

 organisms have led soil biologists to begin the study of soil protozoology 

 in order to determine, if possible, to what extent these organisms influence 

 soil fertility.^ 



In order to facilitate the counting and examination of protozoa, 

 several investigators have cultivated these organisms in artificial cul- 

 ture solutions. Goodey (7) studied the protozoa which were developed in 

 soil extract and dilute hay infusion, but made no attempt to count them. 

 Likewise Martin and Lewin (13) made careful examinations of the organ- 

 isms which they cultivated in an infusion of horse manure. Rahn (15) 

 employed peptone and sugar solutions, thus allowing the organisms to 

 develop in a culture solution of i to 100 dilution for from 7 to 14 days, 

 after which an aliquot of the solution was examined for protozoa. Killer 

 (10) used the dilution method in order to determine the approximate 

 numbers of soil protozoa that were developed in GUtay's, mannite, and 

 peptone solutions. France (6) studied soil protozoa developed in 

 artificial culture solutions and enumerated the organisms from the various 

 soils examined by mixing an average sample of the solution with water 

 and then examining the resulting solution drop by drop. Likewise 

 Cauda and Sangiorgi (2) employed Giltay's, Omelianski's, Hiltner's, 

 peptone, and mannite solutions and determined the numbers of organisms 

 developed by dilution and direct count. In order to find the best culture 

 solution for protozoan development, Cunningham and Lohnis (4) grew 

 these organisms in many different solutions, and later Cunningham 

 employed soil extract and blood-meal extract. The last-named inves- 

 tigator (3) also used the dilution method for the enumeration of the 

 organisms. The results obtained with the dilution method by these 

 investigators have been somewhat irregular. The irregularity in the 

 results secured by the application of this method is shown quite clearly 

 by Cunningham (3). The same irregularity has been experienced by the 

 writer, who found the error to be several hundred per cent in many cases. 



' Contribution from the Laboratories of Biology, Soil Bacteriology, and Soil Chemistry of the New Jersey 

 Agricultural College and Experiment Station. 



' The writer wishes to take this opportunity to express his appreciation to Dr. J. G. Lipman for many 

 suggestions and the information which he has supplied; likewise to Dr. F. E. Chidester for the services 

 rendered throughout the study of this series of problems. 



Journal of Agricultural Research, Vol. IV, No. 6 



Dept. of Agriculture, Washington, D. C. Sept. 15, 1915 



N. J.— I 

 97209°— 15 3 (511) 



