536 MALARIAL FEVER 



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. 98) ; 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. The best results 

 are, however, obtained by one of the Romanowsky methods as 

 described on p. 106. 



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

 number led Ross to devise a method for making their recognition 

 more easy by using blood films of unusual thickness. 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. There is then dropped on it by means of a glass rod a 

 little of the watery eosin used in making up the Romanowsky 

 dye (vide p. 106). This is allowed to act for about a quarter 

 of an hour, and then very gently washed off with distilled water. 

 The Romanowsky methylene-blue solution is then applied for a 

 few seconds and also carefully washed off, and the preparation 

 dried and mounted. The haemoglobin of the red corpuscles is 

 washed out by the eosin solution, and the smaller forms of the 

 malarial parasite stand out as round circles containing the char- 

 acteristic chromatin dots ; and in consequence of the greater 

 number present in an area of unit size as compared with an 

 ordinary preparation their recognition is very easy. For the 

 large forms of the parasite Ross has found it useful to make 

 such a film and, haemolysing the red cells with distilled water, 

 to examine it unstained. The presence of pigment in the para- 

 sites enables these to be readily seen. 



