H. N. RAY AND J. A. IDNANI 269
which is now reduced to a mere ring (Plate XIX,
fig. 14 and Plate XX, fig. 42).
Whether repeated binary fission of one or more
parasites at one and the same time gives rise to
large number of organisms in one red blood
cell has yet to be considered. In our preparations
we came across a single ring form being transformed
into a dividing stage, this being manifested by the
increase in the amount of its cytoplasm and com-
paratively enlarged nucleus. A reference to fig.
13 on Plate XIX, and figs. 33, 34, 36, 38 and 40 on
Plate XX, shows that, while most of the parasites
are in a resting stage, there are some which are in
the stage of division. In all the subsequent stages,
the chief features noted were the central position
of the nucleus and an initial increase, and later
a proportional decrease in the amount of cytop-
lasm as the fission progressed. In the final stage,
as mentioned above, the nucleus migrates towards
the periphery, and the cytoplasm is reduced to a
mere ring. These stages presented themselves
in an orderly sequence, and this pointed to the
conclusion that a single parasite by means of re-
peated binary fission gives rise to 32 daughter
individuals and not 16 as stated in our previous
note [Ray and Idnani, 1938]. The blood corpuscle
containing this large number of parasites ultimately
bursts and liberates the daughter individuals
which measure from 0.5µ to 1.5µ in diameter
(Plate XX, fig. 43). On very rare occasions, com-
ponents of four nuclei were seen in one individual.
In such cases the body of the parasite assumed a
quadrangular form (Plate XIX, fig. 18).
Whatever the shape of the dividing individual,
the general impression obtained by careful exami-
nation of the different stages is that the process
of multiplication is chiefly by binary fission and
not by budding, the latter being common with the
organisms described under the genus Babesia.
Corpuscles carrying the parasites in the initial
stage of multiplication (Plate XIX, figs. 4 to 7)were
not uncommon in the peripheral circulation, but
the erythrocytes showing parasites in the advanced
dividing stage were extremely rare in this situation.
The rarity of such forms in the peripheral circula-
lation can perhaps be attributed to the fact that
such corpuscles became heavy and were therefore
not easily carried to the periphery with the blood
stream. The infected red blood cells, particularly
those which contained the dividing forms, often
became enlarged and irregular in shape. The
dividing forms of the parasite were mostly seen in
impression smears of the spleen, bone marrow and
liver. It was also possible to demonstrate the
organism in sections of these organs (Plate XIX,
figs. 27 and Plate XX, fig. 44). This observation,
however, is not in agreement with the statement
made by Shirlaw [1938] that no ring forms can be
found in the section preparations of P. gibsoni
infected dogs.
(b) Thin elongated forms. Concurrently with
the ring or oval forms, thin elongated forms of the
parasite, which could at once be distinguished
from the former by their slander body and elon-
gated shape, were encountered. The nuclear end
in this form is slightly brbader than its other end
(Plate XIX, fig. 24). Prior to division it appears to
assume an amoeboid shape, and, while still in this
condition, the nucleus shows an evidence of break-
ing up into eight, sixteen or more nuclei. This, how-
ever, was at first thought to be an evidence of
schizogony and was described as such by the
writers in a note to the Indian Science Congress
[1938]. On careful examination, however; we
found that in this form too the multiplication
occurred by binary fission, the only difference
being that the newly-formed daughter individuals
instead of diverging as in the other form remained
very close to each other and thus gave a false
impression of schizogony (Plate XIX, fig. 19).
Individuals, which differentiate themselves from
such a mass, were thin elongated bodies, with the
nucleus situated at one end—this end being slightly
broader than the other (Plate XIX, figs. 20, 21).
Cells containing 32 individuals of this type alone
were encountered in the smears of the spleen and
bone marrow of a heavily infected dog (Plate
XIX, fig. 26). A fully grown individual of this
type measured 2µ to 3.5µ in length and about
0.5µ to 1µ in breadth.
It was not uncommon to find both the forms
described above side by side in the same cell
(Plate XIX, fig. 18). Such parasitized cells were
also met with in the peripheral circulation. Extra-
corpuscular forms of both the types were occa-
sionally seen in the smears made from the internal
organs (Plate XIX, figs. 23, 24). On rare occasions,
the parasite was also seen to assume the shape of an
abnormally elongated spindle (Plate XIX, fig. 22).
SEXUAL DIMORPHISM
From the foregoing account of the morphology
of this organism, it is clear that the parasite ex-
hibits a dimorphic condition, viz. (1) ring or oval
forms and (2) thin elongated forms. These facts
suggest that the two forms represent sexual
dimorphism, a process common to many other
haemosporidia. Provisionally, however, it is pro-
posed to call the round or oval forms females or
macrogametocytes, and the thin elongated forms
males or microgametocytes. This proposal not
only involves the question of the intervention of
an intermediate host* in the transmission of the
disease, but also the question of how the infection
*Swaminath and Shortt [1937] have shown that this
disease is transmitted through the agency of the tick
Haemaphysalis bispinosa.