20 
PROPHYLAXIS OF MALARIA. 
and the chromatin of the plasmodia is obtained. The washing should 
be continued until the specimen becomes a delicate shade of pink or 
pinkish-brown. If distilled water can not be obtained, thoroughly 
boiled water may be used instead. 
Staining reactions with Wright's stain .—In specimens of blood 
properly stained with Wright’s stain, the red blood corpuscles are 
stained a brownish-pink or light salmon, while the various leucocytes 
are stained as follows: The polynuclear leucocytes present a violet 
nucleus with unstained cytoplasm except for light pink granules; 
the mononuclears and lymphocytes have a dark ruby-red or violet 
nucleus, while the cytoplasm is stained blue: the eosinophiles have 
a violet or bluish-violet nucleus, while the granules are stained red; 
the mast cells have purplish-black granules and a dark violet nu¬ 
cleus; while the blood plates stain a ruby-red color, with, in most 
instances, a more or less definite pale lilac margin. 
The cytoplasm of the malaria plasmodia stains a robin's egg 
blue, the vesicular portion of the nucleus remains unstained, while 
the chromatin of the nucleus stains a rubv-red or brilliant violet 
color. The pigment generally appears greenish in color in the ter¬ 
tian plasmodia and almost black in the quartan and estivo-autumnal 
plasmodia. 
The Ross thick-film method .—In suspected cases of malaria in 
which the plasmodia can not be demonstrated by the methods de¬ 
scribed, the thick-film method of Koss should be tried. This method 
will be found of special service in the search for “carriers” of the 
infection and should always be employed in a malaria survey be¬ 
fore a localitv is returned as free from the disease. 
A large drop of blood is placed upon a microscopic slide at or 
near the middle, and is spread with a needle until it covers an area 
about one-half inch in diameter. The smearing may be done with a 
platinum loop, and the film should be made as evenly as possible. 
The preparation is now placed aside and allowed to dry. 
After the film is dry, the slide is placed in a mixture composed 
of 50 c. c. of commercial ethyl alcohol containing 10 drops of com¬ 
mercial hydrochloric acid, and removed when the hemoglobin is 
completely dissolved—a process which is usually complete in from 
10 minutes to half an hour, varying with the thickness of the blood 
smear. The preparation is now fixed and should be washed in run¬ 
ning water for 15 minutes in order to remove the acid, which en¬ 
tirely prevents staining if any considerable amount remains upon 
the slide. After washing, the specimen is allowed to dry and stained 
with Wright’s stain in the manner already described. More stain 
should be used in covering the film, and a longer time should be 
allowed for staining because of the thickness of the film of blood. 
