i8o 



MICROMETRY AND BLOOD PREPARATIONS 



there is a tendency for the polymorphonuclears to be concentrated at 

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



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 par- 

 allel 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 



FIG. 53. 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. 



equal to that described by Daniels. In this the drop of blood is drawn 

 along and not pushed along. The films are even, can be made of any 

 desired thickness by changing the angle of the drawing slide, and there 

 is little liability of crushing pathological cells. Take a small drop of 

 blood on the end of a clean slide. Touch a second slide about 1/2 

 inch from end with the drop and as soon as the blood runs out along 

 the line of the slide end, slide it at an angle of 45 to the other end of the 



