THE MORPHOLOGY, LIFE CYCLE AND PHYSI¬ 
OLOGY OF PLASMODIUM MALARIAE 
(GRASSI AND FELETTI, 1890) 
By MARTIN D. YOUNG and G. ROBERT COATNEY 
U. S. PUBLIC HEALTH SERVICE, COLUMBIA, S. C. 
Morphology, Schizogonous Cycle 
Plasmodium malariae has several charac¬ 
teristics which sharply distinguish it from 
the other human malaria parasites. The 
length of the asexual cycle is 72 hours; a 
small number of merozoites are produced; 
it has the heaviest staining protoplasm and 
produces a large quantity of dark granular 
pigment; the movements of the living para¬ 
site are quite sluggish. 
The morphology of the parasite changes 
as it progresses through its life cycle. The 
youngest stage of the parasite observed in 
an erythrocyte comprises a circle of cyto¬ 
plasm containing a spherical bit of chro¬ 
matin and enclosing a vacuole, the so-called 
‘ ‘ signet ring stage. ” This ring is from one- 
fourth to one-third the size of the infected 
red cell. Although this parasite has denser 
cytoplasm and chromatin than P. vivax, it 
it quite difficult to distinguish between them 
at this stage as both are approximately the 
same size. The distinction between P. ma¬ 
lariae and P. falciparum is easier; in the 
latter the rings assume characteristic bi¬ 
zarre forms and are only about half the size 
of P. malariae. 
P. malariae grows more slowly than any 
of the other human malaria parasites. The 
vacuole disappears after a few hours. In 
the living condition the movement is slug¬ 
gish. Pigment granules begin to appear 
early in its growth and sometimes a granule 
may be found in a late ring stage. The pig¬ 
ment increases rapidly and half grown 
parasites may exhibit 30 to 50 granules. 
This parasite develops more pigment than 
any of the other human malarias. The pig¬ 
ment is in irregular granules, which dis¬ 
tinguishes it from the rod-like pigment of 
P. vivax. When the cytoplasm and pigment 
are together, the latter appears to be brown¬ 
ish-black or even jet black; however, when 
the pigment is seen free of the parasite cyto¬ 
plasm, it often appears amber or yellowish- 
brown. It appears that the heavy cyto¬ 
plasm of the parasite might cut out some of 
the light and give the pigment the dark 
appearance when the two are seen together. 
In the living parasite, the coarse pigment 
exhibits oscillatory motion but little direc¬ 
tional movement. 
As the parasites become larger some of 
the forms may be found stretched out like 
a ribbon across the cell, the so-called ‘ ‘ band 
forms.” These bands are found lying in 
every direction as well as that in which the 
smear was made, and, therefore, it can 
hardly be said that they are the result of the 
directional pressure in making the smear. 
Furthermore, these bands are found much 
more frequently in P. malariae than in the 
other species so that they are considered 
diagnostic. The bands may be seen at any 
time until the parasites practically fill the 
host cell. Quite frequently in these band 
forms the chromatin will be distributed 
along one longitudinal or vertical border, 
with the pigment in a parallel distribution 
on the opposite border. In such eases, the 
chromatin often appears dispersed instead 
of being in a typical concentrated mass. 
At other times, the chromatin and pigment 
may be scattered indiscriminately through¬ 
out the parasite. 
As the parasite matures, its size ap¬ 
proaches that of its host erythrocyte. This 
species of parasite does not cause enlarge¬ 
ment or blanching of the parasitized red 
cell; in fact, sometimes the parasitized red 
cells seem to shrink slightly. 
After about the 54th hour, multiple chro- 
