Smear PreparaUofis from Fluid Material 



General Principles 



Every chapter up to the present has 

 been concerned with the preparation of 

 microscope shdes from whole objects pre- 

 served in as nearly as possible their natu- 

 ral shape. Chapters 10 through 15 will 

 be concerned with the preparation of thin 

 slices or sedio^is of objects. Between these 

 extremes of a whole object and a thin slice 

 there are two types of preparation, which 

 are discussed in the next three chapters. 

 Smears, discussed in this and the next 

 chapter, are exactly what their name indi- 

 cate : they are prepared by smearing some 

 substance on a clean glass slide where it 

 may be fixed, stained, and mounted. 

 Squashes, the name of which is also self- 

 explanatory, are prepared by squeezing 

 either animal or plant materials in such a 

 way that thej^ disintegrate into their com- 

 ponent cells, which may then be studied 

 without reference to the relations which 

 they previously had with each other. 



Smears may either be prepared from 

 fluids or from soUd objects. A separate 

 chapter is devoted to each. The present 

 chapter deals with the preparation of thin 

 layers of fluid so that the cells contained 

 in them may be studied. Three operations 

 are necessary in the preparation of smears 

 of fluids: first, the smearing of the material 

 itself into a layer of the required thickness; 

 second, fixing this layer both to insure its 

 adherence to the slide and to make sure 

 that the contained cells remain in their 

 normal shape; third, staining and mount- 

 ing the fixed smear. Each of these opera- 

 tions will be discussed successively. 



Preparation of the Smear 



The first thing to do in the preparation 

 of a smear is to make sure that chemically 



clean slides are available. The adherence 

 of the smeared material to the slide will be 

 excellent if it is a fluid containing con- 

 siderable quantities of protein (as blood), 

 even if the shde be not clean, but there 

 are many fluids which are used in the pro- 

 duction of smears which will not adhere 

 at all save to an absolutely clean glass 

 surface. Any method may be used for 

 cleaning slides, but for this particular 

 purpose the author prefers to use a house- 

 hold scouring powder, which consists of a 

 soft abrasive together with some detergent 

 agent. This powder is made into a thin 

 cream with water and each slide is then 

 dipped into this cream and stood in a rack 

 to dry. As soon as it has dried the shdes 

 may be returned to a box, preferably each 

 being separated from the other with a 

 thin paper insert. As slides are commonly 

 sold with these paper separators, it is only 

 necessary to take a box and to save the 

 separators when one dips the slide, return- 

 ing them after they are dried to the same 

 box with the same separators. 



Two or three hundred slides may easily 

 be prepared in this manner in a short time 

 and stored against future use. For use the 

 slide is polished with a clean linen or silk 

 cloth. Smears often have to be made at un- 

 expected moments, therefore it is a con- 

 venience to have slides at hand which may 

 be rendered fit for use in a few moments. 



The actual method of smearing the ma- 

 terial varies greatly according to what is 

 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 de- 

 scribed as a type. The material itself may 

 either be taken from the puncture wound 



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