284 APPLIED BACTERIOLOGY 



former are more rarely encountered, and only in certain 

 cases — are much more easily recognised. 



If no parasitic form be found in the first field, pass to a 

 second, a third, and so on, devoting at least half an hour to 

 the examination of the slide before pronouncing definitely 

 in a negative sense on the presence of the parasite. 



Stained Blood Preparations. — Stained preparations are not 

 only useful on account of the confirmation they offer of the 

 appearances seen in the fresh blood, but the advantages 

 they offer owing to their permanent character. The blood 

 is collected as above upon a clean cover-glass, taking care 

 that the drop is a small one ; another clean cover-glass is 

 very gently laid down upon the drop. As soon as the blood 

 has spread out in a uniform layer, the two cover-glasses are 

 drawn apart, and the two. blood films allowed to dry spon- 

 taneously. The film is then fixed by immersion in absolute 

 alcohol and subsequently stained with Lbffler's methylene 

 blue, or double staining may be effected by treating the 

 dried blood first with a 1 per cent, aqueous solution of 

 eosine, which stains the corpuscles pink, and then with 

 Lbffler's methylene blue, which stains the parasites and 

 leucocytes blue. 



The most satisfactory staining method for malarial blood 

 is the use of Chezynsky's solution. This is made by mixing 

 20 parts of a 0*5 per cent, solution of eosine in 70 per cent, 

 alcohol; 40 parts of a saturated aqueous solution of methy 

 lene blue, and 40 parts of water. The solution is filtered 

 before use. The cover-glasses with the blood films, after 

 fixing, should be floated face downwards upon this solution 

 for about one hour. If the stain is warmed to blood-heat, 

 or a trifle over, 20 minutes^ staining will generally suffice. 

 The cover-glasses are then drained, thoroughly washed in 

 distilled water, dried and mounted in xylol balsam. 



