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PROTOZOOLOGY 



slide. Next push the second shde over the surface of the first shde at 

 an angle of about 45° toward the other end (2). Thus a thin film of 

 blood is spread over the slide (3). Let the slide lie horizontally and 

 dry, under a cover to prevent dust particles falling on it and to keep 

 away flies or other insects. If properly made, the film is made up of 

 a single layer of blood cells. 



Thick films. Often parasites are so few that to find them in a thin 

 film involves a great deal of time. In such cases, a thick film is advo- 



FiG. 336. Diagrams showing how a thin blood film is made on a slide. 



cated. For this, 4 to 6 drops of blood are placed in the central half- 

 inch square area, and spread them into an even layer with a needle 

 or with a corner of a slide. Let the film dry. With a little practice, a 

 satisfactory thick smear can be made. It will take two hours or more 

 to dry. Do not dry by heat, but placing it in an incubator at 37°C. 

 will hasten the drying. When thoroughly dry, immerse it in water 

 and dehaemoglobinize it. Air dry again. 



Thin and thick film. Often it is time-saving if thin and thick films 

 are made on a single slide. Place a single drop of blood near the center 



