110 M(tli()(ls for hJ.ntiiiliKitidii (if Snil Protir.dii 



If ordinary coverslips are used for this work it is often difficult to 

 decide which side of the covershp the film is on, particularly if the 

 films have been stored for some time in 70% alcohol. For this reason 

 the coverslips described by one of us in a previous paper ("A note on 

 the protozoa, etc., from sick soils," Roy. Soc. Proc., Vol. 85. 1912, p. 3'.)5) 

 will be found very useful. These are oblong coverslips of which one 

 angle has been cut off. ami they can he procured from Messrs Frazer, 

 of Edinburgh. Messrs Zeiss, or Messrs Angus. It is obvious that no 

 mistake can arise if it is arranged that the film is always on the lower 

 surface of the coverslip wiieii the long sides point away from the worker 

 and the cut corner separates the right long side from the distant short 

 side. 



The methods for the examination of soil protozoa can l)c divided 

 roughly into three categories, (1) methods for the detection and exami- 

 nation of the active fauna in life, (2) methods for the examination of 

 the active fauna on fresh fixed films of a soil, (3) cultural methods. 



(1) Detection of active fauna in life. Up to the present we have 

 found no reasonably successful method for the collection and exami- 

 nation of the active fauna of a soil in a living state. Any method which 

 depends upon the addition of water to the soil must admit of very rapid 

 execution, otherwise there is the danger of protective cysts present in 

 the soil opening, and thus giving a false impression as to the constitution 

 of the active fauna. This danger is probably a very real one in the case 

 of the small flagellates, and especially the resting forms of some green 

 algae, in the case of which a few minutes' immersion in water may make 

 the difference between a resting and an active form. Another difficulty 

 seems to be to obtain films adequately rich in comparison with the films 

 got by fixing the fresh soil by the methods described below, and in this 

 respect it is found that methods which give fair results with one type of 

 soil may break down completely with another. 



All the methods we have used with any success up to the present 

 depend upon the possibility of collecting and retaining some of the 

 protozoa on a surface film. They all seem uniformly bad, and the only 

 consolation in their use is that the other methods we have tried, including 

 the use of the centrifuge, have up to the present given worse results. 



With some rather dry, clay soils, at Rothamsted, fair results were 

 obtained by crumbling a soil into a dish of water, and removing the 

 surface film for the purpose of examination either by floating coverslips 

 on it, or by means of thin wire formed into a circular loop of about 

 }," diameter. 



