AMOEBIC DYSENTERY. 



531 



structures really constitute a stage in the development of the organism, 

 as direct transformation from the one form into the other has not been 

 observed. 



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 thus 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 mem- 

 brane. The amoebae are found in the mucous membrane when ulcers 

 are being formed, but their most characteristic site is beyond the ulcer- 

 ated area, where they may be seen penetrating deeply into the sub- 

 mucous, 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 swell- 

 ing and proliferation of the connective-tissue cells. This action of the 

 amcebse on the tissues explains the character of the ulcers as just described. 

 These lesions are considered by Councilman and Lafleur to be charac- 

 teristic 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. 

 Microscopic examination shows chiefly necrosed and granular cells and 

 debris -resulting from their disintegration, whereas ordinary pus cor- 

 puscles are scanty or may be practically absent. 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. 1 70). They are most numerous 

 at the spreading margin, and this probably explains a fact pointed out 

 by Manson, that examination of the contents first removed may give a 

 negative result, while they may be detected in the discharge a day or two 

 later. The action here on the tissues is of an analogous nature, namely, 



