RELATIONS OF PROTOZOA TO MAN 



73 



the digestive tract: Trichomonas tenax lives 

 in the tartar of the human mouth; and 

 Chilomastix mesnili. Trichomonas hominis 

 (Fig. 37) and Giardia lamblia (Fig. 37) in- 

 habit the intestine. Chilomastix is a pear- 

 shaped organism with four conspicuous fla- 

 gella at its broad anterior end. Its cysts are 

 lemon-shaped. Trichomonas hominis is of 

 similar contour, but bears from three to five 

 anterior flagella besides a longitudinal un- 

 dulating membrane. There is also a central 

 axostyle which protrudes caudally as a dis- 

 tinct tail. Trichomonas never forms cysts. 



Giardia lamblia (Fig. 37) is an odd-look- 

 ing protozoan with two anterior nuclei and 

 a number of backwardly directed flagella. 

 The cell has one flat side by which it may 

 adhere to an epithelial cell. This species 



sometimes causes mechanical interference 

 with absorption, particularly fats; and the 

 presence of large amounts of unabsorbed 

 fats causes diarrhea. The cyst of Giardia is 

 elongate, with four nuclei grouped at one 

 end. Atabrine is an effective drug in the 

 treatment of giardiasis. 



Trichomonas vaginalis is an inhabitant 

 primarily of the vagina and may cause in- 

 flammation of this organ. It closely resem- 

 bles Trichomonas hominis (Fig. 37). 



The largest protozoan found in the hu- 

 man intestinal tract is Balantidium coli 

 (Fig. 38). This large motile organism pene- 

 trates the membrane lining of the colon, 

 where it frequently causes ulcers. It is a 

 definite disease-producing organism and may 

 produce symptoms resembling acute amoe- 



Oo 



Cell mouth 

 Contractile vacuole 



Food vacuoles 

 Micronucleus 



Macronucleus 



Contractile vacuole 

 Anal pore 



Cyst 



Trophozoite 



Figure 38. Balantidium coli, a ciliate parasitic in man. Highly magnified. 



bic dysentery. Infected persons pass large 

 spherical cysts, easily identified by micro- 

 scopic examination. 



The Sporozoa are represented among the 

 intestinal forms by Isospora hominis, a 

 rather rare form, sometimes accused of caus- 

 ing a diarrheic condition. 



PROTOZOA PARASITIC IN 

 OTHER ANIMALS 



Both game and domestic animals harbor 

 a variety of protozoan parasites, which affect 

 directly or indirectly the economic well-be- 

 ing of man. Trichomonas foetus is an im- 



