130 DISEASES OF DOMESTICATED BIRDS 
gathered into a compact circular mass approximately in the center 
of the odcyst (fig. 18 O). The nucleus imbedded in the central mat- 
ter now undergoes division into two and these in turn divide, form- 
ing four daughter nuclei (fig. 13 P). These are surrounded by cyto- 
plasm and separated from each other. As a result four rounded 
bodies are formed within the cyst. These are sporoblasts (fig. 13 Q). 
Later the sporoblast loses its rounded form, becomes oval and is 
inclosed in a cell wall (fig. 18 R). In this form it is termed a 
sporocyst and from it develops a spore which contains two young 
infective parasites or sporozoites. The life cycle is completed by 
the rupture of the odcyst wall in the intestinal tract of the host, 
which releases the spores and the primary infecting sporozoites. 
From experiments made by feeding fowl chicks with coccidian 
odcysts, Fantham concludes that the period for the total life cycle 
of the parasite is from eight to ten days. 
Pathogenicity. Apparently coccidiosis is infectious to all do- 
mesticated and wild birds which are exposed to its causative organ- 
ism. It has been observed in a wide variety of these birds and its 
incidence has been marked by high mortality, especially in those con- 
fined to limited areas. It is highly destructive to young chickens 
and frequently affects baby chicks. Its greatest ravages are seen 
in chickens which have passed the brooder stage and are exposed 
to the infective agent in infected houses or grounds. Limited range, 
as 1s customary in the rearing of domesticated birds, and especially 
in the case of chickens closely confined in large flocks, is conducive 
to heavy infection and high mortality in the event that coccidia are 
present. Next to chickens, pigeons are no doubt most severely af- 
fected. Outbreaks among ducks and geese occur less often as an 
epizootic unless the birds are closely confined, but individual infec- 
tion commonly occurs. 
Birds of all ages are susceptible. Mature birds exhibit a fair de- 
gree of resistance. They may harbor the coccidia and appear nor- 
mal until they become grossly infected, or become weakened through 
other causes to such an extent that their power of resistance is lost. 
Mortality. In chicks affected at the age of two to ten weeks, 
the disease runs a rapid course and the mortality may reach 100 per 
cent in closely confined flocks. In older fowls, the fatalities, while 
not so great, are usually very heavy in those surrounded by unsan- 
itary conditions. Mature hens have a greater power of resistance 
but even among these, severe losses may be observed. The mortality 
is governed by the degree of exposure. 
