7 



Making Smears 



The last chapter was concerned with the preparation of microscope slides 

 from whole objects preserved as nearly as possible in their natural shape; the 

 next chapter will be concerned with the preparation of thin slices of objects 

 or "sections." Between the extremes of a whole object and a thin slice, there 

 is the type of preparation which is discussed in this chapter. This is the 

 "smear," which is exactly what its name indicates; that is, it is prepared by 

 smearing some substance on a clean glass slide where it may be fixed, stained, 

 and mounted. Three operations are necessary in the preparation of smears of 

 fluids: (1) The smearing of the material itself into a layer of the required 

 thickness; (2) the fixing of this layer both to insure its adherence to the slide 

 and to make sure that the contained cells remain in their normal shape; and 

 (3) the staining and mounting of the fixed smear. Each of these operations 

 will be discussed successively. 



Preparation of the Smear. The first thing to do in the preparation of a smear 

 is to make sure that there are some chemically clean slides available. Only mate- 

 rials containing large quantities of protein, such as blood, will adhere to slides 

 that are not perfectly clean. Any method may be used for cleaning slides. For 

 this particular purpose, however, the author prefers to take any household 

 "scouring powder," which consists of a soft abrasive together with some deter- 

 gent agent. The powder is made into a thin cream with water. Each slide is 

 then dipped into the cream and put in a rack to dry. As soon as it has dried, 

 the slide may be returned to a box, preferably separated from the next slide 

 with a thin paper insert. Since slides are commonly sold with paper separators, 

 they may be stored with the separators in the original box. 



Two or three hundred slides may be prepared easily and quickly in this 

 manner and stored for future use. When a slide is needed, the white powder 

 is polished from the surface with a clean linen or silk cloth. Smears often have 

 to be made at unexpected moments, so that it is a great convenience to have 

 slides at hand which may be rendered fit for use in a few moments. 



The actual method of smearing varies greatly according to the material 

 being used. Probably more smears are made of blood than of any other fluid, 

 and the technique for the preparation of these is so well established that it 

 will be described as a type. The material itself either may be taken from 

 the puncture wound directly onto the slide or, as in Fig. 13, removed from 

 the puncture wound with a pipette and transferred to the slide. The drop is 

 placed about a third of an inch from one end of the slide. A second slide, as 



49 



