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tumbler in order to keep them free from dust. The palmar surface of the
patient's finger tip where the prick is to be made is then thoroughly cleaned with
alcohol. The prick is best made with an ordinary surgical needle. If it is made
without hesitation, sharply and not too deeply, no pain will be felt by the
patient ; but even this simple operation requires some practice. The first drop of
blood which appears should be wiped off, and before the second drop is squeezed
out a cover glass should be taken up in the forceps and held ready over the
finger. As soon as the second drop of blood—which should not be larger than
a pin's head—appears, the centre of the cover glass is made to touch it. The
drop of blood comes away on the cover glass which is then quickly laid on to
one of the glass slides. If the operation has been done successfully the blood
immediately spreads out in a thin film between the cover glass and the slide.
A slight tap with the end of the forceps on the upper surface of the cover glass
sometimes assists the blood to spread out more easily, but if the slides and
cover glasses are perfectly clean this should not be necessary. After waiting a
minute or two, the edge of the cover glass may be ringed with vaseline in order
to prevent evaporation. The specimen will then keep good for several hours.
The preparation should first be examined with a one-sixth inch
objective,
and if it is a sucessful one, the red blood corpuscles in many parts of the specimen
will be found to be lying flat in a single layer with their edges nearly touching
each other but not overlapping, and these are the parts of the specimen to be
specially examined for parasites. Nearer the edge of the cover glass the corpuscles
will be found heaped up and overlapping each other. Having found a suitable
field, a small drop of cedar-wood oil is placed on the cover glass and the oil-im-
mersion lens turned on. A substage condenser and a low eyepiece must be
used, and the iris diaphragm should be nearly closed so that only a moderate
amount of light passes through the specimen. If the illumination is too
brilliant the parasites may be easily missed.
A beginner should not at first attempt to find small unpigmented parasites ;
he should search for large pigmented forms, and above all he should remember
(1) that the parasite must be looked for inside a red blood corpuscle, and (2)
that it is a very definite organism which, if once seen, cannot well be mistaken
for anything else.
On searching each corpuscle carefully the observer will presently come
across one in which fine black dots of pigment are seen. On focussing care-
fully he will find that these dots are contained in a transparent mass of pale
protoplasm which is undergoing amœboid movement inside the corpuscle.
After a short time the movements will become less marked and the outline of the
body will become more distinct. Careful watching will convince the observer
that he is looking at a living parasite. Once having found a parasite, the
beginner will know what sort of body to look for, and will easily be able to
educate himself to pick out the smaller forms.
The reason why beginners make so many mistakes over malaria parasites is
partly because they are not thoroughly familiar with the appe ranee of normal
blood, and partly because they do not search in suitable cases at the com-
mencement of their study. The majority of men who are commencing the
subject expect to find parasites in the most unlikely cases,—cases with charts
showing no sign of periodicity or cases of chronic cachexia which have been
drenched with quinine. Even an experienced observer would probably be unable