524 A MANUAL OF BACTERIOLOGY 



evaporation. A little practice is required to judge the right quan- 

 tity of blood. The preparation should be examined with a T V-i nc h 

 oil-immersion lens. 



Examination in the stained condition. To prepare stained films 

 the finger or ear is pricked of the malaria or other blood parasites, 

 e.g. trypanosomes, and a droplet of blood is taken up on the edge 

 of the end of a slide '(the spreader), which is then applied to the 

 surface of a second slide and, holding the spreader at an angle of 

 45, it is pushed along the surface of the second slide so that a thin 

 film of the blood is left behind, and the process is repeated for as 

 many films as are required. A little practice is required to gauge 

 the right quantity of blood. Other methods of preparing blood- 

 films are to deposit a droplet of blood on a cover-glass ; another 

 cover-glass is applied, and the two are separated so that each is 

 smeared with a thin film of blood, or a droplet of blood on a slide 

 may be spread with a cigarette paper, or with the shaft of a needle. 

 Whatever method is adopted, the film is allowed to dry in the 

 air, and may then be fixed (not if Leishman's stain is used). In 

 order to fix, the smears should be immersed in a mixture of equal 

 parts of absolute alcohol and ether for not less than ten minutes, 

 preferably for half an hour ; this gives excellent results. In hot 

 countries a saturated solution of corrosive sublimate may be used. 

 The methods detailed at p. 97 may also be employed. 



Staining is usually carried out with Leishman's stain (No. 12, 

 p. 102). The blood films, unfixed, are flooded with a few drops 

 (5-10) of the stain, which is spread by tilting, and in hot weather 

 the preparation should be covered with a capsule to prevent evapo- 

 ration. After a half to one minute distilled water is added and 

 mixed with the stain, in sufficient amount to produce an abundant 

 precipitate, and the mixture should appear pinkish ; the water 

 should be about double the amount of stain used, and staining is 

 continued for five, or in some cases for ten, minutes. The staining 

 should be continued until the nuclei of the leucocytes are a rich 

 purple when examined with a low power. The film is then rinsed 

 with distilled water, a little distilled water is left on the film, which 

 is watched under the low power until the red corpuscles appear 

 red ; this takes half a minute or more. The water is now tilted 

 off the film, and the slide on edge allowed to dry, or it may be blotted 

 and dried. Fresh films stain better than old ones ; if the films 

 are old, staining with the diluted stain should be prolonged for 

 ten or fifteen minutes and differentiation with distilled water 

 may take five minutes. Jenner's or Giemsa's blood-stain may be 

 similarly used. 



