ONE-CELLED ANIMALS— PHYLUM PROTOZOA 



91 



checks the penetrations of these organisms and thus prevents such serious 

 results. 



The disease caused by this infection is known as amoebic dysentery. 

 The irritation of the colon usually causes a person to have extreme diar- 

 rhea accompanied by general weakness of the body. Examinations of 

 the watery stools reveal thousands of the endamoebae in the active vege- 

 tative state. Also, many of the cells will be seen to have formed cysts 

 by means of which the disease may be spread to other persons. Cysts 



Courtesy General Biological Supply House 



Fig. 7.4. Endamocba histolytica, pathogenic protozoan which causes amoebic dysen- 

 tery Left : active forms found in the stools of an infected person. Right : section of 

 the large intestine of a person who died of amoebic dysentery. Three endamoebae 

 can be seen in the center of the photograph. 



are produced from the vegetative cells by the elimination of water which 

 concentrates the protoplasm and by the formation of a protective cyst 

 wall around the outside. The vegetative cells die rather quickly after 

 they leave the protective warmth and moisture of the body, but the 

 cysts can live a much longer time. 



The cysts may be spread from one person to another through con- 

 taminated food or drinking water. The food may be contaminated by 

 flies that have contacted fecal material from infected persons, or by 

 food handlers that harbor the organisms in their bodies. Many persons 



