BALANTIDIUM COLI I LIFE-CYCLE 



a thin, clear peripheral layer of ectoplasm and a central 

 granular mass of endoplasm. Within the cytoplasm are 

 a kidney-shaped macronucleus, in the concave side of 

 which lies a minute spherical micronucleus, and two con- 

 tractile vacuoles situated as indicated in the figure. 



2. LIFE-CYCLE 



The life-cycle of B. coli is not fully known. Asexual 

 reproduction is by transverse fission involving the mass 

 division of the macronucleus into two apparently equal 

 parts and a sort of mitotic division of the micronucleus. 

 Rapid division sometimes results in the formation of 

 "nests" of small specimens in the tissues of the intestinal 

 wall. Sporulation (Walker, 1909) and budding (Ohi, 

 1924) have been described but have not been satisfac- 

 torily confirmed. 



Encystment may occur in the intestine. The cyst is 

 provided with a double wall secreted by the organism. 

 Conjugation cysts have been described by Brumpt 

 (1913). Small specimens only 30AC in length, that result 

 from rapid division, unite in pairs, secrete a cyst wall 

 about themselves, throw out part of their substance, and 

 then fuse into one. The further history of these cysts is 

 unknown. 



3. HOST-PARASITE RELATIONS 



Viability. The trophozoites of B. coli, according to 

 McDonald (1922), live for only a few hours outside of 

 the host. He found that cooling the intestinal contents 

 of the pig to room temperature causes the organisms to 

 become spherical, in which condition they will live for 

 6 or 8 hours; when kept in an incubator at 37.5° C. they 



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