SOIL PROTOZOA IX SOUTH AFRICA. 



389 



permit, soils from the Transvaal and Natal collected towards the 

 end of the summer (for example, at the end of March, in April, 

 ar>d early May) yielded more kinds of Protozoa than did soils col- 

 lected in the drier winter months, such as July. 



Influence of Pulverisation of Sod. 



Some experiments were undertaken to determine the method 

 of attachment of protozoal cysts to the soil and the effect of soil 

 pulverisation. Tn direct examination of soil, detection of cysts was 

 not easv. The effect of fine pulverisation or trituration of soil in 

 water was to increase the number of cysts discernible by separating 

 them from the soil partices to which they were firmly adherent. 

 Two examples may be cited: — 



(i) A definite quantity, 01 gram, of Grahamstown soil was 

 Aveighed and put in a watchglass with 2 c.c. of water on top of it. 

 The fluid and top layer of soil were examined after ten minutes. 

 The total number of protozoal cysts detected was 7. 



The fluid and soil were then rubbed together with a small 

 glass pestle for two and a half minutes, allowed to stand for ten 

 minutes, and then the fluid and surface layer of soil were again 

 examined. The number of cysts was 11. The material was again 

 returned to the watchglass and the fluid and soil were rubbed 

 together for a further two and a half minutes, allowed to stand 

 for ten minutes, and then re-examined. The number of cysts 

 detected was 17. 



(ii) In another experiment, 01 gram of cultivated dolerite 

 soil from Cedara was put in a small glass tube, 2 c.c. of water was 

 poured on the top, and it was allowed to stand for thirty minutes. 

 The cysts in the liquid and surface layer of soil were counted, the 

 number being 7. 



The soil and liquid were returned to the tube, the soil was 

 well rubbed up for two and a half minutes, a turbid brownish 

 fluid being obtained after standing for fifteen minutes. This fluid 

 and the surface layer of soil were examined, and 16 cysts found. 

 The procedure was repeated as before, and a further examination 

 resulted in 18 cysts being detected. 



Thus, the more finely the soil was pulverised the more readily 

 the cysts became detached from the soil particles and the larger 

 was the number of cysts detected. 



Two cultures were made of equal quantities of the cultivated 

 dolerite soil from Cedara. In one culture soil as dug was used, 

 in the second finely pulverised soil. It was found that trophic 

 Protozoa (such as Ciliates and Flagellates) appeared more quickly 

 in the culture of the finely pulverised soil than in the soil as 

 dug, the periods being one day and three days respectively. 



It is probable that the colloidal complex of organic and inor- 

 ganic compounds more or less saturated with water that surrounds 

 the particles of soil, together with the surface tension of the 

 films, is the cause of the very close adhesion of the 

 Protozoa, either trophic or encysted, to the soil particles. It also 

 affords an explanation of the difficulty of detecting trophic Pro- 



