PREPARATION OF FILMS. 161 
2. Two pair of dissecting forceps. 
3. A needle for taking blood. 
4. A platinum loop having a diameter of about one- 
tenth of an inch is sometimes useful, especially to a 
beginner. 
Method.—The patient having been pricked and the 
first drop of blood wiped away, take up a cover-glass in 
one pair of forceps, holding the glass by its corner, and 
touch the drop of blood with it. In doing so take great 
care not to touch the patient’s skin. There should now 
be a small drop of blood in the very centre of the cover- 
glass. This 1s the difficult step; you must not get too 
*much nor too little blood, or the films will be useless. 
Now take up the second cover-glass in the other pair of 
forceps and place it on the top of the drop in sucha 
position that the corners of the two cover-glasses do not 
correspond. Release the upper cover-glass; it will ap- 
proach the lower one, being drawn thereto by the 
capillary attraction caused by the presence of a small 
quantity of fluid between the two. 
At this stage you will see whether you have taken the 
right amount of blood or no. If you have, the drop will 
spread out, still retaining its circular shape, until it 
approaches the octagon formed by the intersecting 
edges of the two cover-glasses; if you have taken too 
little it will not reach so far; and if you have taken too 
much it will extend further and the upper cover-glass 
will float loosely on the lower. 
It is necessary to lay great emphasis on the fact that 
the cover-glasses must mot be squeezed together, but 
must simply come together by capillary attraction. 
When the drop has ceased to spread take hold of the 
upper cover-glass with the forceps at a corner opposite 
to that of the lower cover-glass which you are still 
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