ENTAMOEBA HISTOLYTICA 39 



it is that E. histolytica is the cause of amoebic dysentery and other 

 diseases, and yet usually " non-pathogenic " : how amoebic diseases 

 are not contracted from persons actually suffering from them : and 

 consequently, how amoebic dysentery and liver abscess come to be 

 endemic and never epidemic in their incidence. For every abnormal 

 individual suffering from dysentery, but non-infective to others, there are 

 dozens of comparatively healthy infected individuals — carriers — who 

 show no clinical signs of infection, but whose amoebae undergo their 

 normal development, and whose cyst-containing faeces are infective 

 to others. 



There can be little doubt that E. histolytica, even when it causes no 

 dysenteric or other recognizable symptoms, must always live at the 

 expense of its host's tissues. Every healthy carrier has the lining of his 

 large bowel more or less ulcerated ; though the ulceration may be, and 

 probably often is, superficial and almost invisible post iiiortem to the 

 naked eye.* But even quite extensive ulceration may exist without any 

 dysenteric symptoms being evident. This is clearly shown by the post 

 mortem findings of Musgrave (1910), Bartlett (1917), and others ; and it 

 is undoubtedly incorrect to suppose — as many still do — that because an 

 infected person does not suffer from dysentery his intestine is therefore 

 not ulcerated. A point of importance in this connexion is the fact that 

 a person may suffer from an amoebic abscess of the liver or other organ 

 without ever suffering from dysentery. Now E. histolytica reaches the 

 liver by way of the portal vein. To get into this the amoebae must 

 traverse the wall of the gut, and to do so they must damage the tissues. 

 Consequently, the parasites must have caused at least some ulceration of 

 the intestine before they gained access to the liver. The case described 

 by Armitage (1919) is particularly interestingf in this respect : for the 

 patient was always, so far as his intestinal infection was concerned, a 

 contact carrier of E. histolytica, who had never suffered from dysentery 

 or other intestinal trouble. But he acquired a typical amoebic abscess 

 of the liver, and when this was almost cured, an amoebic abscess of the 

 brain, from which he died. In his stools the cysts of the parasite were 

 present, and in the abscesses the typical tissue-inhabiting amoebae. Such 

 cases as this show clearly that the contact carrier is not infected with 

 a non-pathogenic strain of amoebae — as some would argue ; and also 

 that ulceration of the intestine may be present in the absence of all 

 dysenteric symptoms. 



Walker (1913), Wenyon and O'Connor (1917), and most other com- 

 petent observers appear to share these views as to the pathology of the 

 carrier condition ; and no other interpretation which has been put 

 forward is, I think, compatible with all the facts. But I shall have 

 occasion to refer to the discrepancies and difficulties in these other 

 interpretations later in another connexion. 



At present there is little to show what percentage of the persons who 

 acquire infection with E. histolytica will become healthy carriers, and 

 what percentage will suffer from amoebic dysentery or other diseases. 

 The only figures are those furnished by the experiments of Walker 



* I have seen — in the cat's intestine — ulceration which is only recognizable with 

 certainty in sections examined under the microscope. 



t I cite this case because it is one in which I was able, through the kindness of 

 Capt. Armitage, to take a personal inteiest. 



