HOST-PARASITE RELATIONS: INTESTINAL PROTOZOA 



cient magnitude to be noticed by the host or his physi- 

 cian. It is well known that whether or not symptoms 

 appear in many parasitic infections depends on the num- 

 ber of parasites present. 



Sections of the intestinal wall of both man and experi- 

 mental animals infected with E. histolytica have revealed 

 large numbers of amoebae in the glands of Lieberkiihn. 

 Here again, functions may be disturbed merely by the 

 presence of the parasites. Amoebae also invade the tis- 

 sues of the intestinal wall. They are supposed to do this 

 by dissolving away the cells with the aid of a cytolytic 

 ferment which they secrete or by pressure due to their 

 rapid multiplication and the consequent blocking of the 

 opening of the glands into which they have migrated. 

 They do not appear to ingest red blood cells or other 

 tissue elements while within the tissues. Continued mul- 

 tiplication of the amoebae and cellular destruction leads 

 to the formation of a nodule which eventually bursts 

 into the intestinal lumen, thus producing an ulcer. Some 

 of the amoebae that escape invade neighboring glands 

 and repeat the process, thus spreading the infected area. 

 At the same time, those that remain in the ulcer continue 

 the destruction of the tissues at the sides and bottom. 

 Further pathological effects result from a continuation 

 of this process. These tissue-invading amoebae are large 

 and never of the precystic type; the latter, as well as 

 cysts, occur only in the lumen of the intestine. What mod- 

 ifications occur in other parts of the body due to the 

 formation of ulcers in the intestine are very little under- 

 stood and their genesis unknown. 



Much of this story, as mentioned above, is based on 



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