Sept. IS. I9IS Soil Protozoa 517 



forms in the soil, but it was probably not until the work of Breal (i) in 

 1896, later by France (6), and by Wolff (19) in 1909, that mention was 

 made of the probable effect which protozoa might have upon soil fertility 

 due to the destructive influence which they might have upon other 

 soil micro-organisms. Then again, the very extensive work on soil 

 sterilization by Russell and Hutchinson (16, 17) in 1909 and 1913 has 

 been carried out for the purpose of showing the effect of heat and anti- 

 septics upon a detrimental factor in the soil, which those authors believe 

 to be protozoa. In 1911 Goodey (7) describes the isolation of various 

 protozoa from the soil and concludes that protozoa are inactive in normal 

 soils. A few years later, however, he (8) concluded that the ciliated 

 forms are present in the soil in the encysted condition and that the 

 amoebae and flagellates act as limiting factors. Martin (12), examining 

 freshly collected soil for protozoa, concluded that the prevalence of 

 protozoa in culture solutions was no indication of their presence in the 

 living state in the soil. Upon the examination of cucumber-sick soil, 

 Martin and Lewin (13) found eight different kinds of protozoa. Amoebae 

 were probably the dominant forms in the soil during examination. 

 Flagellates were very rare. These investigators state that in absolutely 

 saturated soils the ciliates may play an active part as a bacteria check 

 but that "it is difficult to beheve that they can exercise an important 

 role in a sick soil-bed." Russell and Petherbridge (18) are also of the 

 opinion that the factor which keeps down the numbers of bacteria in 

 cucumber- and tomato-sick soil is biological. Killer (10), Rahn (15), 

 Cunningham and Lohnis (4, p. 600), and later Cunningham (3) grew soil 

 protozoa in various culture solutions and noted a great difference in the 

 development of these organisms in artificial media. 



Cunningham (3, p. 22) concludes that "the results given in this section 

 prove conclusively that the soil protozoa, in solution at all events, exer- 

 cise a very decided limiting effect on the numbers of bacteria. " 



DEVELOPMENT OF PROTOZOA IN ARTIFICIAL CULTURE SOLUTIONS 



In this study it was the object of the writer: 



(i) To compare the difference in numbers and species of protozoa 

 developed in different culture solutions. 



(2) To compare the protozoan development from varying amounts of 

 soil. 



(3) To compare the protozoan development from moist and drv soil. 



(4) To compare the protozoan development from different greenhouse 

 soils. 



A large sample of clayey soil having a moisture content of 25 per cent 

 and upon which alfalfa was grown in 19 14 and then composted to a 20 

 per cent manure, was collected from a compost bin in the greenhouse. A 

 portion of this soil was dried for three days at 35° C. Into 200 c. c. 



