THE MICRO-ORGANIC POPULATION OF THE SOIL 289 



A protozoological survey of the soil has been begun, and 

 in order to give it as permanent a value as possible the inves- 

 tigations are not confined to the narrow issue whether soil 

 protozoa do or do not interfere with soil bacteria, but they 

 are put on the broader and safer lines of ascertaining whether 

 a trophic protozoan fauna normally occurs in soil, and if so, 

 how the protozoa live, arid what is their relation to other soil 

 inhabitants. 



The first experiments by Goodey dealt mainly with ciliates 

 (iio<z) and indicated that these protozoa were present only as 

 cysts. Subsequent . investigations, however, by Martin and 

 Lewin (191) established the following conclusions : 



1. A protozoan fauna in a trophic state normally occurs in 

 soils. 



2. The trophic fauna found in the soil differs from that 

 developing when soil is inoculated into hay infusions, 1 and 

 vice versa the forms predominating in the hay infusions do 

 not necessarily figure largely in the soil. 



3. The trophic fauna is most readily demonstrated, and is 

 therefore presumably most numerous, in moist soils well sup- 

 plied with organic manures, e.g. dunged soils, sewage soils 

 and especially glass-house " sick " soils. 



The enumeration of the protozoa in the soil is carried out 

 by means of a dilution .method somewhat similar to that 

 adopted for soil bacteria. It is already clear that amcebae 

 and flagellates are present in at least thousands per grm. of 

 soil, while ciliates can be found only in hundreds. Some of 

 the organisms appear to be new to science, and many of them 

 are of considerable interest. 



The presence of protozoa is not peculiar to British soils : 

 they have been found in Egypt, 2 France, 3 Italy, 4 Germany, 6 

 the United States, and elsewhere. Methods have been devised 



1 This is not necessarily true of all artificial media. 



2 Ronald Ross and D. Thomson, Egyptian Sand Amoeba (Proc. Soc. Med. 

 Sect. Epidem., 1916, 9, 33), and H. Sandon (Rothamsted). 



3 In the Rothamsted laboratory. 



4 A. Cauda and C. Sangiorgi (Turin), Cent. Bakt. Par., 2 Abt., 1914, 42, 393.. 



5 R. Oehler, Arch.f. Protistenkimde, 1916, 37, 175; 1919, 40, 16. 



19 



