640 MALARIAL FEVER 



protoplasm of the haemic mononuclears in blackwater fever. The 

 significance of the appearance is not at present elucidated, but 

 they might be of a protozoal nature. 



Methods of Examination. The parasites may be studied by 

 examining the blood in the fresh condition, or by permanent 

 preparations. In the former case, a slide and cover-glass having 

 been thoroughly cleaned, a small drop of blood from the finger 

 or lobe of the ear is caught by the cover-glass, and allowed to 

 spread out between it and the slide. 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 evaporation. 

 For satifactory examination an immersion lens is to be preferred. 

 The amoeboid movements are visible at the ordinary room tem- 

 perature, 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, which are then fixed and stained by one of the 

 Romano wsky methods, as described on p. 114. When such 

 stains are not available, the dried films should be fixed by one of 

 the methods described on p. 94 and then stained by methylene- 

 or thionin-blue. 



The fact that in many cases the parasites may be few in 

 number led Ross to devise the " thick film process " for making 

 their recognition more easy. Here about as much blood as is 

 used in a haemoglobin determination (20 c.mm.) is taken on a 

 slide, and, being spread out only so much as to occupy the area 

 of an ordinary cover-glass, is allowed to dry. The haemoglobin 

 is removed by treating with distilled water and the preparation is 

 then stained by one of the Romanowsky methods ; the parasites 

 can then be readily found. Ross and Thomson have recently 

 modified the method for enumeration purposes. They take a 

 definite small amount of blood, say 1 c.mm., and discharge it on 

 a slide as one or more droplets, which are dried and treated as 

 above. The whole blood is then carefully searched with an oil 

 immersion lens with the aid of a movable stage, and the total 

 number of parasites present are counted. 



