112 MrtliiKh for Exinniitaliou of Soil Proto'.o<( 



absolute, followed by teipeneol and balsam. Teipencol will be found 

 veiy convenient for tliis purpose as it clears from a much lower per- 

 centage of alcohol than oil of cloves or oil of cedar. 



(2) Esaniitmtinn of active fauna in fresh fixed films. In the j)repara- 

 tion of fresh films from soil to which a ii.xative has been added we once 

 again depend upon the surface films. For some obscure reason not 

 yet understood, if certain fixatives are added to a (luantitv of soil a 

 surface film is formed which contains an unknown but probably variable 

 proportion of the active fauna of the soil, cysts, diatoms, moulds, algae, 

 and bacteria. In the production of this result, it is certain that the 

 contained air in the soils exercises a favourable influence in bringing 

 the animals to the surface film, and really good results cannot be 

 expected l)v this m(>tliod from a soil which is absolutely water logged. 

 Of the fixatives we have tried up to the present, picric alcohol (i.e.. 

 50 "/„ saturated solution picric acid in water, plus 50 % rectified spirit), 

 and corrosive alcohol {i.e., 50 % saturated solution corrosive sublimate 

 in water, plus 50 % rectified spirit) have given us the best results. 



The ix'st method appears to be to place the soil in a porcelain dish, 

 and pour enough of the fixative through a funnel to the bottom of the 

 soil layer until the soil is just covered. The film so obtained can be 

 taken off on coverslips floated on the surface of the liquid. 



Of these two fixatives picric alcohol appears to give rirlier utkI more 

 abundant films, particularly as regards small organisms, in sandy soils, 

 whereas corrosive alcohol appears to work better on clay soils, and is 

 more efficient in collecting thick-pellicled amoebae. 



The efficiency of the film formation is frecjuently increased by 

 slightly shaking the dish immediately after the addition of the fixative. 

 The following is a good method for staining and mounting the film so 

 obtained. 



Pioric Films 



Corrosive — 2 minutes Corrosive Films 



70 % alcohol plus a few 



drops of I., in KT 5 minutes 



IJiatilled water .5 minutes 



Haemalum 5 minutes 



Tap water Till blue 



70 % alcohol .') minutes 



Eosin in absolute alcoliol 3 minutes 



Absolute alcohol I 1 minute 



Absolute alcohol TT 1 minute 



Xylol I 2 minutes 



Xylol II 1 niiiiut* 



