230 TROPICAL MEDICINE AND HYGIENE 



In man encysted amoebae may be found in apparently 

 healthy stools, but the hosts from time to time have attacks 

 of diarrhoea or dysentery and then the active amoebae are 

 present in the stools. The diagnosis therefore of the 

 encysted forms is important both for diagnosis and 

 treatment. 



Some amoebae can be cultivated from stools, but it is 

 doubtful if these are obligatory parasites, and these may 

 be merely encysted forms of non-parasitic amcebas which 

 have been swallowed and passed through the intestinal 

 canal. 



Amoebae parasitic in the internal organs of man are 

 sometimes called Entatncebce. Morphologically there is 

 no real difference between these and other amoebae 

 beyond the absence of a contractile vesicle. 



The problem is to a large extent one of species, as it is 

 only the pathogenic amoebae that are of importance to 

 us. The others can be cultivated outside the intestine. 



Morphological characters are only adequate when the 

 characters during the whole life-cycle are considered. 

 The characters in the encysted stage are the most 

 constant. 



There are said to be several species, one occurring 

 in the mouth, A. buccalis, in some persons with dental 

 disease, and two at least in the large intestine (vide Table). 

 Of these, the A. coli, or Entamceba coli, is not found in 

 other parts of the body and the life-cycle is as described 

 by Schaudinn. According to the same author it is dis- 

 tinguishable by its appearance as the ectosarc or ecto- 

 plasm is not visible as a distinct layer, and the nucleus is 

 large and rich in chromatin, so that it stains deeply in 

 stained preparations. This amoeba is not considered to 

 cause disease. It may be present in the small intestines 

 as an active motile amoeba, and only the encysted forms 

 found in the stools unless there is diarrhoea. 



The other intestinal amoeba, Entamceba tetragena 

 (f histolytica), has a more distinct ectoplasm and the 

 pseudopodia are entifely formed by it at first, so that 



