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Oriental Sore 
sporozoites of the haemogregariiie. Reinfection of the dogs must be 
constantly taking place, and sporozoites finding their way to the spleen 
or bone marrow. The probable course is that a sporozoite enters a 
mononuclear cell of the spleen or the bone marrow, increases in size, and 
eventually gives rise to a variable number of large merozoites which 
escape from their cyst and proceed to produce the small sexual forms 
which find their way into the peripheral blood. In favour of this view is 
the fact that it is very usual to find the cysts containing the small 
sexual foiins grouped together in threes or fours in such a manner as to 
suggest that a sporozoite had recently produced three or four merozoites 
near this spot, that these have escaped from their cyst and settled down 
near together to produce the small sexual forms. 
The process of formation of the small sexual forms takes place in a 
manner very similar to that of the merozoites with the difference that 
the nuclear divisions proceed very much further. The details are the 
same, and even up to the last division in suitably stained specimens the 
karyosorne can be detected in the middle of the chromatin area (PI. XVI, 
figs. 0 and 14). The number of nuclei is very large and there are 
produced a corresponding number of small sexual forms (Text-fig. 8). 
With the rupture of the cyst they escape and enter the mononuclear 
cells of tlie blood where they appear as the familiar haemogregarines in 
the leucocytes. 
The host cell during both these processes of reproduction is reduced 
to a thin envelope surrounding the parasite. The nucleus of the host 
cell, very much flattened and altered, is seen at one side of the cyst 
(PI. XVI, figs. 2, 8, 14). It is probable that in addition to this covering 
derived from the thinned out host cell the parasite secretes a covering 
of its own. These cysts are of some resistance, for in the squash 
preparations of the fresh organs they are not easily ruptured, and in 
the staining of smears which have been fixed without drying, the stain 
only penetrates with difficulty. The details of the contents of the cyst 
are only clearly made out in sections where the cysts have been opened 
at some point. 
The fully formed cysts in the spleen and bone marrow are about 
25-30 fjb in diameter. The size of the cysts varies very little whether 
they contain the large merozoites or the numerous small sexual forms. 
