SOIL PROTOZOA IN SOUTH AFEICA. 391 



of Protozoa and Bacteria approximating to the normal or natural. 

 Certain other workers appear to have laid too much stress on 

 artificial culture-media, which unduly favour bacteria, and prob- 

 ably produce an artificial pabulum for Protozoa on which they 

 have to subsist or else die out. In artificial media it is probable 

 that the numerical proportions of Protozoa and Bacteria are altered, 

 as also are their biological activities. Hence some of the inferences 

 made by certain workers in other parts of the world, using bacterio- 

 logical media, may need emendation for South African conditions. 



From the few observations made up to the present it seems 

 that relatively tenacious loam soils contain the greatest numbers 

 of Protozoa and that sandy soils contain fewest organisms. Cul- 

 tures of acid soils have in some cases contained more genera than 

 alkaline or neutral soils, the acidity or otherwise of the samples of 

 soil being determined by litmus compression tests. It seems prob- 

 able that the colloids of the soil may play an important part in 

 the regulation of the activities of the protozoal fauna. Partial 

 sterilisation of the soil in South Africa by solar radiat-'on is also 

 a limiting factor, and any form of partial sterilisation limits Pro- 

 tozoa according to Waksman. 



In addition to Protozoa, certain Metazoa have been observed 

 by us in cultures of South African soils. Rotifers, Chaetonotus 

 maxim us (belonging to the Gastrotricha), Nematodes and Oligo- 

 chaetes have been found. This is in contrast to the finding in New 

 Jersey soils, where Nematodes were the only Metazoa observed. 



In water cultures of almost all the South African soils 

 -examined diatoms were found, and these may serve as food for 

 some of the Protozoa present. It is known that in some cases the 

 soil samples were obtained from areas known to be flooded at 

 •certain times of the year, or to be subjected to irrigation. 



It will be noted that many of the Protozoa found in cultures 

 of soil are of similar genera and species to those found in natural 

 fresh waters, but the relative numbers and proportions of the dif- 

 ferent organisms observed in soil cultures are different from those 

 •of normal aquatic protozoal faunas- 



Summary. 



A summary of a paper such as the present one is difficult, 

 tooth on account of the nature of the subject, with its many and 

 varying factors, and the stage of the work. Some of the principal 

 results are as follows : — 



(1) Examination by direct observation and by water culture 

 of a number of South African soils from the Cape Province, the 

 Transvaal and Natal, under conditions of cultivation varying from 

 virgin soil to heavily cultivated sugar land, has shown the presence 

 of genera of Protozoa belonging to the Sarcodina, Mastigophora 

 and Ciliata. The genera and species vary considerably, both 

 with the locality and with the degree of cultivation of the soil. 



(2) Few trophic Protozoa were detected in fresh non-water- 

 logged soils, the organisms occurring mostly in the encysted or 

 resistant condition. 



