MORPHOLOGY. LIFE CYCLE AND PHYSIOLOGY OF P. FALCIPARUM 
43 
zoites withdraw from the peripheral circu¬ 
lation. Marchiafava and Bignami (1894) 
remarked on the tendency of the adult 
forms to accumulate in the internal organs. 
Some authors have observed a tendency of 
the infected erythrocytes, particularly those 
containing older “ring” forms, to adhere 
both to one another and to the vascular 
endothelium. To this characteristic Thom¬ 
son and Robertson (1935) attributed the 
collection of the infected cells in the inter¬ 
nal organs. Marchiafava and Bignami 
(1901) considered that such aggregation 
was due to loss of elasticity of the infected 
red cell with consequent irregularity of the 
surface resulting in difficulty in traversing 
the capillary bed. On the other hand, in¬ 
fected erythrocytes do not get held up in 
the cutaneous capillaries so that there may 
well be another factor involved of which we 
are not yet aware. At any rate it is pre¬ 
sumably in the visceral circulation that 
schizogony occurs, as we rarely see evidence 
of it in the peripheral circulation. In fatal 
pernicious forms of falciparum malaria 
with, for example, cerebral involvement, it 
is common to find all stages of schizogony 
in the cerebral capillaries, which may be 
blocked by infected erythrocytes. 
With further development, the parasite 
tends to become more compact and the chro¬ 
matin becomes more centrally located, al¬ 
though the latter is usually not in a compact 
mass, but on the other hand assumes very 
irregular shapes. Much less of the vacuole 
is evident and soon none remains. 
In smears from a falciparum-infected pla¬ 
centa we have observed a very compactly 
formed stage evidently just prior to the on¬ 
set of schizogony. This form is no larger 
than the oldest rings one sees in the periph¬ 
eral circulation. It has no vacuole and its 
more or less spherical area appears about 
equally divided between chromatin and 
cytoplasm, yet it contains a mass of pig¬ 
ment, the area of which may be a third as 
large as that of the cytoplasm. 
Typical of the schizogonous stage in this 
species is the tendency of the pigment to 
form one compact mass. This is evident 
when only one division of the chromatin has 
taken place, and such a block of pigment is 
most usually situated eccentrically even 
though schizogony may be complete. The 
chromatin masses of the very young schi- 
zonts are notably irregular in shape and 
size and cytoplasmic divisions are not evi¬ 
dent. It is not until schizogony nears com¬ 
pletion that some semblance of uniformity 
appears. The mature schizonts of P. falci¬ 
parum are characteristically smaller than 
those of P. malariae; some have been ob¬ 
served that did not occupy more than a 
quarter of the area of an erythrocyte. Oc¬ 
casionally more than one segmenter may be 
found in a single red cell. 
Gametocytes. Although a variety of 
shapes may be met with, the falciparum 
gametocyte most frequently has the con¬ 
tour of a sausage and it is unfortunate that 
it was given the name “crescent.” As a 
matter of fact a crescent-shaped gametocyte 
is relatively uncommon and the shape of 
the mature stage is rarely rounded as is the 
case in the other species. This latter fact 
convinced some observers that P. falci¬ 
parum ought to be placed in a different 
genus designated Laverania. Majority 
opinion, however, is probably against its 
segregation on the basis of a differently 
shaped gametocyte. 
Characteristic of this species of plas- 
modium is the fact that not only does it 
undergo schizogony and. sporulation in the 
internal organs but also, for the most part, 
the early stages of gametogeny. 
Because of the wave-like release of gam¬ 
etocytes into the peripheral circulation, 
usually about the end of a period of clinical 
activity and when the trophozoites are very 
low in number, one might get the impres¬ 
sion that practically all parasite production 
had been given over to gametogeny. Thom¬ 
son (1914), and Thomson and Robertson 
(1935), however, felt that the. evidence is in 
favor of their requiring about ten days for 
development from the ring form. These 
authors also feel that the gametocytes have 
a restricted life span, perhaps only a few 
days, in the peripheral blood and that their 
appearance over a long period means con- 
