102 PKACTICAL PABASITOLOGY 



slip of filter paper, which should be moistened with water if Miiller's 

 mixture is used for fixing, but with 30 per cent, alcohol if alcohol is 

 used. The glass slides are placed on the plate and covered with 

 a large glass bell or with a sheet of glass. 



After a few days, the fixing mixture is drawn off by means of 

 filter paper introduced under the cover-glasses ; the specimens are 

 rinsed several times with water, and weak (20 to 25 per cent.) alcohol 

 is then added, the specimens being allowed to soak in it for twenty- 

 four hours. The weak alcohol is next replaced, first by 30 per cent., 

 and then by 40 per cent, alcohol, the specimens being allowed, after 

 each change, to remain for some time in the damp chamber. Finally; 

 a drop of glycerine mixed with 40 per cent, alcohol in equal parts 

 is introduced at the edge of the cover-glass. The specimens should 

 be exposed to the air, or covered with a large glass bell, when the 

 water and alcohol will slowly evaporate, leaving the glycerine, more 

 glycerine being added from time to time at the edge of the cover- 

 glass. The objects will finally lie in pure glycerine and will be found 

 sufficiently transparent for examination under the microscope. They 

 should be mounted in glycerine-gelatine in the manner described 

 above. The cover-glass is raised, the glycerine removed, and the 

 glass slide in the immediate neighbourhood of the specimen cleaned 

 with filter paper soaked in weak alcohol. Glycerine-gelatine is 

 liquefied in a spatula over a flame and added to the specimen, which 

 is immediately covered with a clean cover-glass. 



Objects fixed with weak alcohol should be treated in a similar 

 manner, omitting, in this case, the water stages. Nematodes pre- 

 pared in this way will sometimes keep good for twenty years. Looss 1 

 also recommends the glycerine method for preserving Nematodes. He 

 uses 70 per cent, alcohol, to which, in the case of delicate specimens, 

 2 to 3 per cent, of its volume in glycerine is added, though a propor- 

 tion of 5 to 10 per cent, may be employed for the robuster forms. 

 The mixture is heated before use and is poured over the specimens, 

 which should be arranged upon glass slides or in shallow vessels. 

 The worms will die almost immediately and will straighten themselves 

 out, though Trichocephales, Trichosoma and Strongylides, with longi- 

 tudinal striation of the skin, usually roll themselves up. This can be 

 prevented only by mechanical means. 



If Nematodes which have been killed in glycerine-alcohol are placed 

 in shallow dishes, together with a sufficient quantity of the liquid, and 

 covered with a large glass bell, the alcohol will slowly evaporate, leav- 

 ing the worms in pure glycerine. The process may be hastened by the 

 use of an incubator. 



1 Looss, Zool Anz., xxiv, 1901, p. 315. 



