MICROSCOPICAL EXAMINATION. l7l 



and the index finger, and the covers are gently sHd apart, care 

 being taken to keep them parallel until they are entirely separated. 

 The two covers, v^^ith films up, are now laid on a piece of paper to 

 dry, and a second pair are prepared in the same manner. If more 

 than four covers are desired, a fresh puncture should be made. 

 As soon as the films are dry, they may be placed in a small enve- 

 lope and properly labelled. If they are stored in a dry place, they 

 will remain unchanged for a long period. It is better, however, to 

 fix them immediately. If water or any staining fluid was to be 

 applied before fixing, most of the corpuscles would be washed off 

 the cover, and from those that did remain the haemoglobin would 

 be removed, leaving only the invisible stroma. 



With regard to fixing the corpuscles, says Dr. Piffard, the best 

 method, and one which his own experience leads him to prefer, is 

 with heat rather than any of the other methods that have been 

 employed. For the past year, for this purpose, he has used an 

 electric heater controlled by a rheostat. The covers are heated 

 gradually to about 2 2 5°F. and then maintained at this for an hour 

 or more. When the covers are taken from the oven, they are 

 allowed to cool gradually and thoroughly before staining. 



When ready to stain the covers, they are placed film up on a 

 plate of glass, and covered each with the eosin solution. This is 

 left on for two or three minutes, and washed off with distilled 

 water. When the covers are dry, the methylene-blue solution is 

 applied in the same manner ; and when this is washed off, and the 

 covers are thoroughly dry, they are ready for preliminary examina- 

 tion. 



The microscope is arranged vertically, with a clean slide on 

 the stage, and the cover is placed on it, film down and without 

 any intervening medium. Alongside of it, if it is desired, another 

 cover is mounted in balsam and the two are compared. The dif 

 ference between the two is so striking and absolutely in favour of 

 the dry cover that Dr. Piffard thinks the balsam would be rejected 

 for this purpose. This examination must, of course, be made with 

 a dry lens. A No. 7 Leitz answers very well, but an eighth of an 

 inch or a tenth of an inch objective, with a numerical aperture 

 approximating 0*90, is still better. 



If the examination with the dry lens does not give all desired 



