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PREPARATION OF FILMS
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exudes. Then gently, with finger and thumb, squeeze the finger-pad and express a second minute droplet of blood; this should be very small—no larger than a pin's head. Touch the droplet lightly with the centre of a cover-glass, taking care that the latter does not come into contact with the skin, and immediately drop the cover-glass on the slide. No pressure should be used to cause the blood to spread out. If glasses and skin are quite clean, the blood will at once run out in a
Fig. 16.—Microphotogram showing the necessary disposition of blood-corpuscles in slides for examination for the plasmodium. To the right of the white blood-corpuscle in the centre of the field a red blood-corpuscle three-fourths filled with a tertian parasite is visible (From microphotogram by Dr. Cosens.)
very fine film. It is sometimes more convenient to obtain the blood from the lobe of the ear or, in children, the great toe.
Several preparations should be made, the requisite blood being obtained by renewed gentle compression of the finger-tip.
After waiting a few minutes to allow the blood to spread out completely between the glasses, it is well to ring the preparations with vaseline. This will effectually stop all movement, all evaporation of
