December, 1954 ]
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exerts a lysing effect on the oocystic wall and the steida body of the sporocyst,
thus releasing sporozoites. It is also conceivable that even if oocysts are damaged
or cracked in the gizzard, the sporozoite can still remain unaffected in the acid
medium of stomach by virtue of the presence of acid polysaccharides in their body.
In vitro liberation of sporozoites was obtained with trypsinic digestion of the
oocyst wall and it was observed that sporozoites were liberated without the oocyst
wall being damaged mechanically. This observation confirms the findings of
Smetana [1933]. It is, therefore, difficult to subscribe fully to the views of Goodrich
[1944] that physical damage to the oocyst wall is essential for the liberation of sporo-
zoites by the enzymatic activity of trypsin.
The fact that second generation merozoites contain a fair quantity of mucopoly-
saccharides explains the successful establishment of infection by Levine [1949]
and Ray (unpublished data) in chicks by feeding them with freshly liberated
merozoites. Presence of these acid polysaccharides in their bodies ensures their
safe passage through the acidic medium of proventriculus.
Some aspects of host-parasite relationship. From the foregoing discussion it
becomes clear as to how the defensive powers of both the host and parasite are
invoked in caecal coccidiosis. Caecal tissue tolerates the parasite upto the end of
the third day when it seems not to 'mind' the latter's presence. This is evident
from the absence of any local tissue reaction. But as the second generation schi-
zogony is consummating to differentiation of merozoites, mucopolysaccharides have
appeared in it in large quantities. Profuse bleeding has started, blood and in-
flammatory exudate which is literally perfusing each cell of caecal wall, possesses
highly coagulating power. This is a very strict measure host has adopted against
the invader. But the latter too has not lagged behind in its protection. Second
generation merozoites are 'born' endowed with strongly anticoagulant (hydrotropic)
mucopolysaccharides. Thus, the forces of the host and parasite have counterpoised
each other. If the host survives, the parasite does not cause any further harm to
the former, hastens to leave the host in a couple of days. As gametogony is pro-
ceeding host mobilises cellular reserves to clear away the debris and reorganise the
damaged tissue.
It has been mentioned earlier that mast cells swarm the caecal tissue when the
violent struggle between the host and parasite for preservation of its species is going
on. Host has stepped up its efforts through increased thrombin content ; the
latter being a double-edged weapon can act both ways against the parasite, as
well as it can threaten the existence of the host. The host has profitably directed
this potential weapon against the invader, as it has protected itself, somehow or
other, to prevent against the intravascular clotting of its own blood. As small a
quantity as 0.5 ml. of caecal fluid when injected into a healthy adult bird
cause its sudden death. The host has protected remarkably either through some
humoral readjustment or by providing some local barrier against absorption of
inimical caecal exudate. Appearance of mast cells in large numbers in caecal wall
at this juncture is significant, as they manufacture a potent anticoagulant-heparin.
In case of death of the host, parasite has also not reached any fructuitous stage,
and exterminates itself along with the former. No doubt Nature favours survival