MALARIAL FEVER. 527 



It ought to be of such a size that only a thin layer is formed. A ring of 

 vaseline is placed round the edge of the cover-glass to prevent evapora- 

 tion. For satisfactory examination an immersion lens is to be preferred. 

 The amreboid movements are visible at the ordinary room temperature, 

 though they are more active on a warm stage. With an Abbe condenser 

 a small aperture of the diaphragm should be used. 



Permanent preparations are best made by means of dried films. A 

 small drop of blood is allowed to spread itself out between two cover- 

 glasses, which are separated by sliding the one on the other. The films 

 are then allowed to dry. A very good method is that of Manson, who 

 catches the drop of blood on a piece of gutta-percha tissue (a piece of 

 cigarette-paper also does well), and then makes a film on a clean slide 

 by drying the blood over the surface. The dried films are then fixed by 

 one of the methods already given (p. 90), or by placing in absolute 

 alcohol for five minutes (Manson). The films thus prepared and fixed 

 may be stained for two or three minutes in a saturated watery solution 

 of methylene-blue or in carbol-thionin-blue (p. 101) ; the solutions must 

 be carefully filtered (especially the latter), and the films must be washed 

 well after staining. They are then dried and mounted in balsam. In 

 the case of thionin-blue, sharper results are obtained by dehydrating in 

 alcohol and clearing in xylol before mounting. A double stain may be 

 obtained by staining first with .5 per cent solution of " alcohol-soluble " 

 eosin in methylated spirit for two minutes, then washing in water and 

 drying ; thereafter the blue stain is used as above ; the blood corpuscles 

 are stained red, the parasites and nuclei of the leucocytes blue. 



The structure of the parasites is specially well brought out by the 

 following method of Rd. Muir. The films are fixed in saturated solution 

 of corrosive sublimate for a few seconds, and are then washed well in 

 running water. They are then stained with haemalum for ten minutes, 

 washed well, and again stained for about, the same time in a saturated 

 watery solution of methylene-blue; they are then washed in water, 

 dehydrated, cleared in xylol, and mounted in balsam. Here also eosin 

 may first be used as a contrast stain ; but the method as just given is 

 -specially good for picking out the parasites in the blood. The chromatin 

 of the parasites is coloured a violet-blue, the protoplasm a pure blue. 



Romanowsky Method. For studying details in the structure, this 

 method has been extensively applied. It depends on the principle that 

 when " ripened " methylene-blue is mixed with eosin a new compound is 

 formed which has a special affinity for the chromatin of the malarial para- 

 site, staining it a bright red. It is to be noted, however, that the method 

 only succeeds with certain kinds of methylene-blue and eosin. There 

 are various modes of making and applying the stain : we give two recom- 

 mended by Leishman. 



