DIFFERENTIAL DIAGNOSIS OF MALARIAL PARASITES 
51 
smears require longer washing. The slides 
are stood on end to dry, never blotted. An 
electric fan may speed the drying, but di¬ 
rect heat is not recommended, since some of' 
the excess stain which might flow from the 
smear, may be dried upon it and cloud this 
background. 
Rapid staining. The time consumed in 
staining a thick film for diagnosis has been 
a drawback to its general use, hut a com¬ 
bination of Wright and Giemsa stains has 
been devised recently, which reduces stain¬ 
ing time to ten minutes, without detracting 
from the desired coloration (Michelson and 
Wilcox 1940). The stain is prepared by 
dissolving 1.515 gm of Giemsa powder (Na¬ 
tional Aniline and Chemical Company, Inc., 
N. Y.) in 100 cc of glycerine (using heat 
and avoiding absorption of H 2 0). When 
this is dissolved, 100 ec of Wright’s stain 
solution, previously made by adding 2 gm 
of Wright’s powder (National Aniline and 
Chemical) to 1000 cc methyl alcohol and 
aging for at least one month, is added and 
the mixture is allowed to stand over night. 
The next morning an additional 800 cc of 
the aged Wright stain solution is added. 
The amount of stain needed for a few days 
is filtered into a small bottle and is ready 
for immediate use. 
For staining the solution is diluted 1 part 
to 1-0 parts of neutral distilled water and 
poured over the slides in a staining dish. 
Ten minutes are allowed for staining, then 
the stain is flushed from the dish and the 
slides washed for one minute with neutral 
distilled water, after which they are air- 
dried and examined. 
Staining smears in bulk. Where large 
numbers of slides carrying thick smears are 
to be stained, time may be saved and uni¬ 
formity in the quality of staining assured 
by a simple method described by Barber 
and Komp (1929b). The slides are made 
into blocks of as many as 25, by placing 
pieces of cardboard an inch square and 
about 1.2 mm thick between the slides at the 
ends opposite the thick films, compressing 
the alternating slides and squares, and 
winding around that end of the block an 
inch wide strip of heavy paper which is se¬ 
cured with a strong rubber band (Komp 
1933). The outer slides in the block should 
be reversed with the film side “in” to pre¬ 
vent the wet smears from being scraped off 
in the staining process. By this method 
hundreds of slides may be stained in bulk 
and consumption of stain solution dimin¬ 
ished by using a container of the exact size 
necessary to hold the number of blocks to 
be stained. 
Examining smears. For examining blood 
films the oil immersion lens is used. Thick 
films are searched with a low power (pref¬ 
erably 5 x or 6 x) ocular, while any uncer¬ 
tain object may be scrutinized with the 10 x 
ocular. The low power eye-piece gives a 
larger field, greater illumination and clarity 
of color and outline. It lessens eye strain 
by giving a feeling of distance. The 10 x 
ocular enlarges the object and brings the 
field closer. 
Use and advantages of both thin and 
thick films. The thin film is ideal for the 
study of the morphology of the individual 
parasite, for identification of stages and 
species and suffices for diagnosis if the in¬ 
fection is heavy. It also gives the accom¬ 
panying blood picture. It dries quickly, 
can be stained in from 5 to 10 minutes, and 
is ready for immediate examination. How¬ 
ever, it has the great disadvantage of fail¬ 
ing to reveal parasites when density is low. 
Parasites are found most easily along the 
outer edges and in the tails of the smears. 
The thick film is a concentration method, 
particularly valuable for diagnosis and, 
where large numbers of slides are to be ex¬ 
amined, is a method of necessity rather than 
of choice (Green 1931). It quickly reveals 
the sparse or scanty parasites of new or 
chronic cases for the practitioner and gives 
a more accurate idea of the malaria inci¬ 
dence in a survey by greatly increasing the 
number of positives found in single slide 
examinations. It has been estimated that 
the amount of blood covered per micro¬ 
scopic field is increased from 10 to 50 times 
over that in a thin film field, hence ex¬ 
amination time is cut drastically (Sinton 
and Banerjea 1925). Practice and experi¬ 
ence are necessary to become proficient in 
