374 SOIL PROTOZOA IN SOUTH AFRICA. 



by partial sterilisation are complex, as several factors are operating 

 simultaneously. The existing bacterial equilibrium of the soil 

 seems to be disturbed by such treatment. Russell and Hutchinson 

 considered that untreated soil contained a factor, not bacterial, 

 limiting the development of bacteria, which factor was inhibited 

 by antiseptics or heat. This limiting factor was then presumed 

 to be the Protozoa in the soil, and so arose the "protozoan theory 

 of soil fertility." However, the original contention of Russell 

 that Protozoa limit the number of bacteria in the soil cannot yet 

 be considered as proved, as a crucial test is still wanting. Russell 

 and Hutchinson also thought that excessive numbers of Protozoa 

 in soil may be the cause of "soil sickness." 



Regarding work actually done already on soil Protozoa, it 

 seems almost impossible to make definite general statements. 

 Martin and Lewin worked on the subject in England especially 

 about the time of the beginning of the Great War, to be precise, 

 during the period 1912 to 1915. Goodey (1911-1916) published 

 some results obtained from work done at Rothamsted. Cutler 

 is a still more recent worker there. In the "United 

 States, Kopeloff and Coleman (1917) published an interest- 

 ing review on soil Protozoa and soil sterilisation, while Fellers and 

 Allison (1920) recorded results from studies on New Jersey soils. 

 Again, Cunningham (1915), working at Leipzig, published some 

 results on the relations between soil Protozoa and bacteria in labora- 

 tory cultures. From the observations of these authors it seems 

 that the majority of Protozoa ordinarily occur in the soil in the 

 encysted state. They would need to be often active to destroy 

 bacteria. As to culture solutions, the conditions therein are dif- 

 ferent from those found in the soil, as was suggested by Martin. 

 Koch (1915) states that "it is probable that the results produced 

 by adding the soil to tap water more nearly represent the con- 

 ditions as they are found in the soil." Koch also states that "the 

 development of soil Protozoa in artificial culture solutions varies 

 with the kind of media employed." 



From the foregoing it will be seen that many views are 

 prevalent in respect to the relation of soil Protozoa to their 

 environment, and that much more work is necessary before final 

 conclusions can be obtained. Also, it is highly probable that it will 

 not be possible to generalise regarding soil Protozoa for the whole 

 world, there being too many varying factors concerned. 



Material ane Methods. 



An endeavour has been made by the present writers to 

 ascertain and briefly describe the Protozoa found associated with 

 various types of South African soils. Observations at the present 

 stage of the investigation have been of necessity largely confined 

 to living material. The present is the first attempt to investigate 

 soil Protozoa in South Africa, and so must, of necessity, be pre- 

 liminary in character. 



Representative soils were collected from sugar and banana 

 plantations, vineyards, orchards, gardens, agricultural plots, moun- 



