VACCINE-THEKAPY 53 



fugalizing the capsule, and where need be the serum may 

 be pipetted off into a small tube for further use. 



Slides, and how to make Blood-Films. 



It is most essential that glass slides should be free from 

 grease ; this is done by boiling in lysol, then in soda, next 

 in strong acid, and washing out in spirit. 



If a slide is greasy, it is obvious one cannot obtain a per- 

 fectly even film ; and where one is making a blood-count, 

 for reasons of accuracy it is essential that the objects in 



Fig. 28. — Slide, showing Blood-Drop. 



the field should be evenly distributed. By rubbing the 

 surface of the slide with emery-paper, a mechanical rough- 

 ness is produced, which facilitates an even distribution of 

 the elements in the fluid. 



In making a film, it is necessary to ascertain which is the 

 concave and which the convex side of the slide, for it is 

 obvious, to get a good spread, we must place our film on the 

 convex surface. To find out which is which, rotate the 

 slide on a flat smooth surface. On one face it will not spin 

 (concave) ; on the other it will (convex) . 



To make a blood-film, place a drop of blood as blood, 



