326 PRINCIPLES OF SOIL MICROBIOLOGY 



protozoa in the soil was carried out by Goodey 52 who concluded that 

 ciliates are present in the soil only in an encysted condition and can, 

 therefore, not function as a factor limiting bacterial activity in the soil. 

 Martin 53 found that smaller amoebae and flagellates play the most im- 

 portant part in the phenomena of sick soils, while the limiting factor as 

 regards the activity of protozoa in the soil is the average quantity of 

 water. Subsequent investigations 54 demonstrated that a protozoan 

 fauna normally occurs in the soil in a trophic state ; this trophic fauna is 

 most readily demonstrated in moist soil well supplied with organic 

 matter, like heavily manured soils, sewage soils and especially green- 

 house "sick" soils; the forms predominating in the soil are not neces- 

 sarily the same as those that develop on artificial media (hay infusions) 

 inoculated with soil. 



A series of preparations of trophic amoebae, thecamoebae and flag- 

 ellates were made 54 by the methods described above. Flagellates 

 were found 55 to be the most numerous and the only active forms in moist 

 soils; however, amoebae were not looked for. According to Crump 

 and Cutler, 56 flagellates, amoebae and thecamoebae are present in large 

 numbers in a trophic condition in the soil; the fauna increasing with an 

 increase in the content of organic matter in the soil. 



Various American investigators 57 believed that the protozoa exist 

 in the soil mainly in a non-trophic state. Koch concluded that protozoa 

 do not exist in normal field soils or even in soils where the moisture con- 

 tent is somewhat above normal; in greenhouse soils containing much 

 organic matter and with a high moisture content, a few living protozoa 

 were present. The protozoa were found to become active in the soil, 

 whenever the moisture content rises considerably above the normal; 

 both moisture and organic matter were found to be the principal limit- 



52 Goodey, 1911-1915 (p. 323). 



63 Martin, C. H. The presence of protozoa in soils. Nature (London). 

 1913, 111. 



" Martin and Lewin, 1914-1915 (p. 318); Goodey, 1916 (p. 323). 



65 Waksman, S. A. Studies on soil protozoa. Soil Sci., 1, 1916, 135-152; 2: 

 363. 1916. 



66 Crump, 1920 (p. 328); Cutler, D. W. Observations on soil protozoa. Jour. 

 Agr. Sci., 9: 430-444. 1919. 



67 Sherman, J. M. Studies on soil protozoa and their relation to the bacterial 

 flora. Jour. Bact., 1: 35, 165. 1916; Koch, G. P. Soil protozoa. Jour. Agr. 

 Res., 4: 511-559. 1915; 6: 477-4S8. 1915; Soil Sci., 2: 163. 1916; Fellers, C. 

 R., and Allison, F. E. The protozoan fauna of the soils of New Jersey. Soil 

 Sci., 9: 1-25. 1920. 



