146 



MICROMETRY AND BLOOD PREPARATIONS 



PREPARATION AND STAINING OF DRIED FILMS. 

 When preparations are desired for a differential count, Ehrlich's 

 method of making films is to be preferred as the different types of 

 leukocytes are more evenly distributed. In making smears by spread- 

 ing, there is a tendency for the polymorphonuclears to be concentrated 

 at the margin while lymphocytes remain in the central part of the film. 



FIG. 51. Blood technic. i, 2, 3, Method for making blood smear on slide; 

 4, U tube for resting slides while staining; 5, slide showing grease pencil marking, 

 marking prevents stain from overflowing; 6, method for drawing apart cover 

 glasses in making blood smear. 



In Ehrlich's method we have perfectly clean dry cover-slips. Take 

 up a small drop of blood without touching the surface of the ear or finger. 

 Drop this cover-glass immediately on a second one and as soon as the 

 blood runs out in a film, draw the two cover-slips apart in a plane 

 parallel to the cover-glasses. Slide them apart. Ehrlich uses forceps 

 to hold the cover-glasses to avoid moisture from the fingers. 



Of the various methods of spreading films on slides there is none 



