388 SOIL PROTOZOA IN SOUTH AFRICA. 



With regard to viability, Ciliates last longer in a culture than 

 any other class of Protozoa. For example, Paramoecium aurelia 

 appeared in a culture and was still present in abundance 190 days 

 after, other Protozoa having disappeared. 



We know from direct observations that daily variation in 

 numbers of any one organism occurs in a given quantity of soil 

 culture. Counts were made of t lie numbers of Actinophrys sol 

 and Paramoecium aurelia found in 1 c.c. of certain cultures of 

 soil. The daily counts for Actinophrys sol over a short period 

 were I, 15, 19, 40, 4, 13, 12, 7, 20. In the case of Paramoecium 

 aurelia the daily counts were 48, 34, 31, 32, 38, 29, 15, 7, 10, 13. 

 Cutler and Crump (1920) have shown daily variation in the num- 

 ber of active Flagellates in soil cultures from Broadbalk, Rotharn- 

 sted, England- 



Environmental Effects. 



Some observations were made to endeavour to determine the 

 ■effects of variation in environment on the Protozoa in the soil. 



Influence oj Temperature. 



Cultures of soil maintained at 37°C. and 45°C. compared with 

 those kept at room temperature (about 15°C. to 20°C.) showed 

 that room temperature enabled Protozoa to flourish better. 



f/i flue nee of Light. 



A series of observations were made to determine whether 

 •darkness had a retarding or accelerating effect on the development 

 •of Protozoa in soil cultures. It was found that there was little 

 difference in the results obtained with cultures of soil kept in the 

 •dark and those kept in the light, but in the case of a culture of 

 Mayville soil Protozoa appeared rather earlier as motile forms 

 when the culture was kept in the dark (six days as contrasted with 

 nine days)- 



Influence of Types of Soil. 



In regard to numbers of Protozoa associated with different 

 types of soil, dark relatively heavy loam, such as is found at 

 Sydenham, Cedara (black vlei soil), and Onderstepoort showed 

 good results, while sandy soils such as those collected at Kimberley, 

 Rosebank (Cape), and Johannesburg (Houghton Estate) were the 

 least productive in respect to Protozoa. This appears to corrobor- 

 ate the results obtained by Waksman, that the amount of orgjnic 

 matter is a limiting factor to Protozoa. 



As a rule, the number of Protozoa obtained in cultures w as 

 greater when the sample was taken near the surface cf the soil, 

 and the number of Protozoa decreased with the depth at which the 

 sample was taken. We are investigating the matter further. 



Influence of the Season of the Year. 



The season of the year appears to have some influence, at any 

 rate, in some cases. Thus, as far as the present observations 



