136 AMEB.E 



normally found in water or soil, may pass through the intestine 

 uninjured, and these are the ones which have commonly been ob- 

 tained in cultures from faeces. In the third place infection with 

 Endamceba histolytica does not by any means cause dysentery 

 in all cases; in fact, it may be said that in a normal infection 

 there is sufficient resistance on the part of the host so that no 

 appreciable harm results from the attacks of the parasites. The 

 injury done to the tissues is repaired rapidly, and while a certain 

 amount of ulceration probably exists in practically all cases, 

 it may not be sufficient to cause dysentery. Individuals 

 who thus harbor amebae without being greatly inconvenienced 

 by them are the so-called " carriers " of the disease. It is prob- 

 able that only a small percent of infections, possibly only 10 per 

 cent, actually give rise to dysenteric symptoms. The carriers 

 constitute the principal means of dispersal of the parasites, since, 

 to protect themselves against the reactions of the host, the amebae 

 are constantly encysting, and the cysts are constantly being lib- 

 erated with the faeces. In acute cases only free amebse, which 

 cannot infect other individuals, are passed; convalescents, how- 

 ever, usually become carriers for variable lengths of time, and 

 may frequently suffer relapses. 



The Disease. Experiments made by Walker and Sellards 

 in feeding ameba-infected material to animals and human vol- 

 unteers showed that dysenteric symptoms, if they appeared, oc- 

 curred in from 20 to 94 days, averaging about two months. The 

 most marked symptom is an acute diarrhea in which the stools 

 consist largely of blood and mucus. In a typical case from Ala- 

 bama a patient passed as many as fifteen or twenty stools in an 

 hour. This condition had been going on for years, recurring 

 about three or four times a year, lasting a month at a time. In 

 the intervals between these attacks the symptoms were mild and 

 the patient passed only two or three stools a day. Sometimes 

 the attacks are more regularly chronic, or may recur at long in- 

 tervals. Often the dysentery is accompanied by evening fever 

 and anemia from loss of blood in the bowels. 



Instead of producing ulcers on the mucous surface of the large 

 intestine such as occur in bacillary dysentery, the amebae com- 

 monly work deeper into the muscular linings of the intestines. 

 Local swellings first appear, followed by an ulceration of the 

 mucous membrane. This produces a portal for the entrance of 



