646 AMOEBIC DYSENTERY 



who has cultivated an amoeba with characters corresponding to 

 those of E. histolytica and no one, so far as we can find, has 

 been able to cultivate the E. tetragena. Most of the organisms 

 artificially cultivated by different observers form cysts of 

 12-15 JJL in diameter, the whole organism becoming encysted. 



Distribution of the Amoebae. As already stated, they are 

 usually found in large numbers in the contents of the large 

 intestine in tropical amoebic dysentery. They also, however, 

 penetrate into the tissues, where they appear to exert a well- 

 marked action. In this disease the lesions are chiefly in the large 

 intestine, especially in the rectum and at the flexures, though 

 they may also be present in the lower part of the ileum. At 

 first there are seen local swellings on the mucous surface, chiefly 

 due to a sort of inflammatory gelatinous oedema with little 

 leucocytic infiltration; soon, however, the mucous membrane 

 becomes partially ulcerated, more or less extensive necrosis of 

 the subjacent tissues occurs, and gangrenous sloughs result. The 

 ulcers thus come to have irregular and overhanging margins, and 

 the excavation below is often of wider extent than the aperture 

 in the mucous membrane. The amoebae are found in the mucous 

 membrane when ulcers are being formed, but their most 

 characteristic site is beyond the ulcerated area, where they may 

 be seen penetrating deeply into the submucous and even into 

 the muscular coats. In these positions they may be unattended 

 by any other organisms, and the tissues around them show 

 cedematous swelling and more or less necrotic change, without 

 much accompanying cellular reaction beyond a certain amount 

 of swelling and proliferation of the connective-tissue cells. This 

 action of the amoebae on the tissues explains the character of 

 the ulcers as just described. These lesions are considered to be 

 characteristic of amoebic dysentery. 



As a complication of this form of dysentery, liver abscesses 

 are of comparatively common occurrence. They are usually 

 single and of large size ; sometimes there are more than one, and 

 occasionally numerous small ones may be present. The contents 

 are usually a thick pinkish fluid of somewhat slimy consistence, 

 and are largely constituted by necrosed and liquefied tissue with 

 admixture of blood in varying amount. In such abscesses 

 associated with dysentery the amoebae are usually to be found, 

 and not infrequently are the only organisms present, no cultures 

 of bacteria being obtainable by the ordinary methods (Fig. 187). 

 They are most numerous at the spreading margin, and this 

 probably explains a fact pointed out by Manson, that examina- 

 tion of the contents first removed may give a negative result, 



