50 MANUAL OF HUMAN PROTOZOA 



or diarrhoeic faeces contains the trophozoites and occa- 

 sionally cysts, but the formed faeces cysts only. Man 

 becomes infected with the ciliate by taking in viable cysts 

 through mouth. 



Trophozoites 



1. Living specimens. The large protozoan (Fig. 13, l) 

 is ovoid in form. The entire body is covered by numerous 

 slightly obliquely longitudinal rows of cilia by means of 

 which the organism swims about actively. Its size varies 

 considerably, but the average specimens are 48-80n long 

 by 30-60m broad. In slowly moving specimens, a short 

 narrow peristome may be seen near the anterior end, which 

 is lined by somewhat coarser cilia. The cytostome is located 

 at its posterior end and is continuous with the cytopharynx 

 through which solid food particles are taken in. The food 

 particles are of various kinds, including the host's intestinal 

 cells, erythrocytes, and leucocytes. Faecal debris of various 

 types which occur abundantly in the gut lumen, are also 

 ingested. The food vacuoles are found in various parts 

 of the bodv. The cytoplasm is granulated. Near the posterior 

 tip of the body, there is a narrow slit, the cytopyge, through 

 which indigestible solid matter is thrown out. Unlike the 

 other groups of protozoa already mentioned, this ciliate 

 possesses contractile vacuoles, one near the center of the 

 body and the other near the cytopyge. There are two nuclei, 

 of which the large macronucleus is usually visible as a 

 refractile sausage-shaped body. 



2. Stained specimens. In the stained individuals (Fig. 

 13, 2) the structures seen indistinctly in life, may be clearly 

 visible. The macronucleus is stained black and conspicu- 



