202 PROTOZOAN PARASITISM 



The motility of the organism is free swimming for- 

 ward with slow rotation, the locomotive cilia waving 

 rapidly and rythmically, the organism remaining of 

 constant shape, although it is plastic and may flex 

 and elongate in pushing its way through compact 

 debris. 



Multiplication is by transverse binary fission, the 

 micronucleus dividing by mitosis, the meganucleus 

 amitotically (Dobell, 1921), the cytoplasm constrict- 

 ing transversely and forming two offspring, the pos- 

 terior one necessarily forming new anterior parts 

 and both undergoing more or less reorganiza- 

 tion. It has been cultivated by Barret and Yar- 

 borough (1921) in a medium composed of 1 part 

 of inactivated liquid human blood serum to 16 

 parts of 0.5% sodium chloride solution, incubated 

 at 37"C. 



The cyst, formed as the organism passes down the 

 colon, is more rounded or ovoid, and has a definite 

 wall. The body loses its food bodies and vacuoles 

 and becomes compact and granular. It shows more 

 or less cilia and other characteristic features in the 

 newly formed cyst, in fact it still revolves for a short 

 time within the thickwalled space. Older cysts may 

 show only the shell, the body, and macronucleus of 

 the organism. The cyst measures 45 to 65 microns. 

 It survives exposure for some time outside the body 

 in a moist state. 



The active form may usually be seen at any time 

 in feces of the infected, varying in number and ac- 



