Protozoa in Relation to Soil Bacteria. 



305 



The soil was given this treatment in preference to toluening followed by 

 heating as used in the earlier experiment because it was found that the 

 latter treatment did not eradicate all the amoebae and flagellates. Agar plates 

 inoculated with small quantities of the heated soil showed no amoebae or 

 flagellates after a week's incubation and from this it was concluded that all 

 the protozoa had been killed off. The 800 grm. of heated soil were divided 

 into two equal portions of 400 grm. and to one of these 5 per cent, of 

 untreated soil was added and thoroughly mixed with it. Both lots were 

 bottled in the usual way, the mouths of the bottles being furnished with 

 cotton-wool plugs. The water content of all three lots, Untreated (IT), 

 Heated (H), and Heated phis 5 per cent, untreated (H + 5 per cent. U), was 

 20 per cent, by weight. 



The protozoal counts giving the approximate numbers of organisms per 

 gramme of soil are set out in the accompanying Table. 





Untreated. 



^os. 

 per gramme. 



Heated (H). 



Nos. 

 per gramme. 



(H + 5 per cent. U.) 

 Nos. per gramme. 



At start. 



At start. 



At 

 start. 



After 

 19 days. 



After 

 44 days. 



After 

 92 days. 



Ciliates — 

















100 



None 



5 









Rhizopods — 

















3000 



>) 



150 



1000 



5000 



30,000 





50 



31 



5 



100 



200 



2,000 



Gephyramoeba delicatula 



20 





1 



10 



20 



500 



Chlamydophrys sp. ? 



20 



>> 



1 







20 



Flagellates, sps. ? 



1000 



>> 



50 









The following ciliates cropped up so irregiilarly in the cultures of the untreated soil that no 

 real estimate could be formed of their numbers ; only a few species were present per gramme of 

 soil: — Colpoda cucullus, Col. maupasii, JSnchelys sp. ?, Chilodon sp. ?, Gonastomum affine, and 

 Pleurotricha sp. ?. 



The periodical bacterial counts are set out in the Table on p. 306, and 

 their graphic representation is shown in fig. 3. 



Considering now the curves for the bacterial counts, we notice that the 

 usual rise in the (H + 5 per cent. U) soil, reaching its culmination at 50 days, 

 is followed by a drop at 85 days, whilst the (H) curve during the same 

 period continues to rise. In the protozoal counts we find that the 

 rhizopoids have multiplied enormously in numbers during the same period, 

 the Amoeba Umax reaching 30,000 per gramme 7 days after the numbers of 

 bacteria have become depressed. The other organisms mentioned in the 

 Table also show evidence of marked activity ; but I wish to emphasise 



