CHAPTER LVIII 



TECHNIQUE OF BLOOD EXAMINATIONS FOE PROTOZOA 



SLIDES and cover glasses must be scrupulously clean, and are best 

 kept in covered glass jars which are. dust-proof. For most purposes 

 stained preparations on slides are satisfactory and much easier to 

 handle than cover glasses. 



In all investigations, both wet and dry preparations should be 

 made ; some practice is, of course, necessary to obtain satisfactory ones, 

 thin enough to show details. As Manson says, in looking for dates 

 on coins, one would not pile one coin on top of another ; so, in search- 

 ing blood cells for parasites, it is necessary to have the cells lying 

 flat, and in a single layer. Wet preparations are made with a drop of 

 blood not much larger than the head of a pin, on which a cover glass 

 is dropped, and gently pressed down; it is advantageous to lute the 

 margin of the cover glass with warm vaseline (warmed by holding 

 the camel's hair pencil over a flame for a few seconds) to prevent 

 evaporation and consequent currents under the cover glass. A prop- 

 erly sealed wet preparation may be examined at intervals during 

 several days, and this is often necessary in studying movements and 

 the life cycle. Malarial parasites, trypanosomes and others are quickly 

 detected by their movements. 



Stained preparations are necessary for the study of details of 

 structure, and for clinical work are invaluable, since smears may be 

 collected at the bedside, and examined later at home, either by day- 

 light or artificial light. In general, a one hundred watt concentrated- 

 filament nitrogen bulb will be found the best source of illumination 

 for the study of both living and stained protozoa. The Welsbach 

 mantle, acetylene gas or even a kerosene lamp are satisfactory sub- 

 stitutes. At times a color screen, made by interposing a round, glass 

 flask, filled with diluto copper sulphate solution, between the light and 

 the mirror, will prove advantageous. It is particularly in the South 

 and in the tropics that artificial illumination has been most valuable. 

 To prepare stained preparations, a small drop of blood from the 

 ^ar is placed on a slide near one end, while with another clean slide 



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