198 The Philippine Journal of Science 1915 
Muehlens," in an investigation of malaria in Emden, Germany, 
used the thick-film dried and stained unfixed in Giemsa’s stain in 
the usual dilution. He compared the thick- and thin-film method 
by examining for the same period of time (at first ten then five 
minutes) thick and thin preparations from each person. He 
found both thick and thin positive one hundred thirty-one times; 
and the thick positive, but the corresponding thin negative, one 
hundred two times. 
Masterman ** successfully used the thick-film method in the 
investigation of latent malaria in Palestine. He used the method 
of Muehlens. 
In our own work, dealing largely with latent malaria in which 
the parasites are often very few, we have found the thick-film 
method invaluable. In many preparations a parasite will be 
found only after many fields of the thick film have been searched, 
and in a comparatively small percentage of our cases only a 
single ring, plasmodium, or crescent could be found in the entire 
preparation. When a parasite was found in these scanty in- 
fections, we made it a rule to search for other parasites for 
confirmation unless the character of the first one found also 
was beyond doubt. Doubtful parasites are sometimes found in 
thin preparations as well as thick, and the thick offers the 
advantage of giving a better chance of finding a second parasite 
for confirmation. 
In some preparations a part of the red corpuscles containing 
malarial parasites failed to lake out and stood out conspicuously 
against the background, so that they could readily be found and 
their species determined. This behavior of the parasitized cor- 
puscle, by no means constant, was noted in both tertian and 
zestivo-autumnal infections. 
A matter of much importance in the examination of blood 
smears for malarial parasites is the time necessary to give to 
the examination of a preparation before declaring it negative. 
In our work, where thousands of preparations had to be ex- 
amined by only two persons, a saving of time and eye strain was 
of vital importance. 
In all the preparations from three towns, and in the greater 
part of those from a fourth, we carefully noted the time given 
to examination before a preparation was declared negative, and 
we also noted the time required to find the first parasite in the 
8 Beih. z. Arch. f. Schiffs- u. Tropenhyg. (1912), 16, 46. 
“ Journ. Hyg. (1913), 13, 49. 
