DISTRIBUTION OF THE AMCEB^.. 529 



which is very thin and well marked off from the former. 

 The blunt processes which are protruded in amoebic move- 

 ment are composed of the ectoplasm (Fig. 125). By the 

 amoebic movements slow locomotion may be produced. 

 The amoebae often show vacuoles in their substance, and 

 may contain numerous red corpuscles (which appear to 

 undergo digestive liquefaction), also bacteria, etc. There 

 is a single nucleus which lies in the central part of the 

 organism and usually measures about 6 to 8 /A in diameter. 

 It is round or oval and contains a nucleolus. In the 

 living condition the nucleus is invisible or is faintly seen, 

 but becomes very evident on the addition of acetic acid, 

 etc. The amoebae break down pretty rapidly outside the 

 body, and examination of the dysenteric stools twenty-four 

 hours after being passed usually fails to detect any of them. 

 It is only on one or two rare occasions that the process of 

 division of the amoebae has been observed and described. 



By some there have also been described encysted forms. 

 These are of smaller size, about i o to 15 /><,, with a well- 

 marked capsule, sometimes showing a double contour and 

 a central protoplasm in which a nucleus may or may not 

 be visible. It is still doubtful, however, whether these 

 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 dysentery. They also, however, 

 penetrate into the tissues, where they appear to exert a 

 well-marked action. They 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 more or less necrotic change without 

 much accompanying inflammatory reaction. In this way 

 the ulcers are lined by sloughing tissue, and have often an 

 34 



