190 FAMILY: AMCEBIDiE 



large numbers of cysts without showing any symptoms whatever. In 

 view of the recent successful culture of E. histolytica by Boeck and 

 Drbohlav (1925) in egg media, it appears possible that the amoebse may 

 actually live and multiply on the surface of the intestine without giving 

 rise to any lesions. It may be that the infection of many symptomless 

 carrier cases is of this type, and that the precystic amoebae and cysts are 

 produced by amoebae living on the surface of the mucosa. 



As regards the fate of encysted amoebae, there are two views. The 

 one which maintains that an amoeba which has once encysted in the gut 

 is unable to leave its cyst in the large intestine of the same host appears 

 to be in accord with the behaviour of parasitic Protozoa generally. 

 According to this view an encysted amoeba, in order to develop further, 

 must pass out of the intestine and be ingested by another or the same 

 host, so that the cyst may come under the influence of the digestive fluids 

 of the small intestine. A corollary to this is that if all the amoebae in 

 an individual could be induced to encyst, an automatic cure would result, 

 for all the cysts would have to be passed from the body. It is evident, 

 therefore, that it is just as incorrect to suppose that any case is resisting 

 treatment because of the impermeable cysts in the intestine as it would 

 be to conclude that a case of ankylostomiasis was not cured because the 

 eggs of the worm were too resistant. In the one case cure is effected 

 by killing the amoebae which produce the cysts, and in the other by killing 

 the worms which produce the eggs. In either case the presence of cysts 

 or eggs in the stool is an indication that the organisms producing them are 

 still present in the intestine, and that treatment has so far failed to kill 

 the organisms, and not that treatment has failed to kill the cysts or eggs. 

 According to the second view, though the majority of cysts must neces- 

 sarily escape from the intestine, some hatch in the large intestine before 

 they escape, so that the encysted stage can be regarded as a resistant one. 

 There is no evidence that this actually takes place in the large intestine 

 of man, though Sellards and Theiler (1924) have succeeded in infecting 

 kittens by injecting them per rectutn with material which they claim 

 contained only encysted forms of E. histolytica. Dr. Drbohlav informs 

 the writer that he has been able to confirm this observation, which has 

 been repeated by Hoare (1926). The writer has observed in stained 

 preparations cysts of E. histolytica which appeared to have ruptured and 

 to have developed hernia-like protrusions. It is just possible that this may 

 be a natural process, and represents the escape of amoebae from the cyst. 



An individual who is in the carrier condition may at any time revert 

 to one of acute amoebic dysentery. An infected person frequently suffers 

 from periodic attacks of acute amoebic dysentery when only the large 

 tissue-invading forms are present in the stool. Between the attacks, 



