36 THE AMOEBAE LIVING IN MAN 



ferment which first dissolves them. Schaudinn's name " histolytica " is 

 most appropriate for this parasite ; but his description of the amoebae 

 forcing their way through the tissues and dislocating the cells by means of 

 their tough and powerful pseudopodia appears to be unfounded.* Good 

 sections show clearly that the amoebae apply themselves to the tissues, 

 which then break down ; and the organisms thus come to lie in pools of 

 histolysed tissue which they evidently absorb as nutriment. As already 

 noted, they may also ingest red blood corpuscles or fragments of cells, 

 but this is probably the exception rather than the rule. Their chief food 

 is, in all probability, derived from the destroyed tissues, but it is absorbed 

 and not bodily ingested in the manner typical of amoebae. In acute 

 amoebic dysentery, when much blood is present in the intestinal 

 contents, a large proportion of the amoebae passed in the stools may 

 contain red corpuscles : but in sections of intestinal ulcers the proportion 

 is, in my experience, considerably less. 



A belief that E. histolytica depends, in some mysterious way, upon 

 certain bacteria with which it lives in " symbiosis," is continually 

 encountered in the literature. It appears to have arisen at a time when 

 it was believed — from the work of Kartulis, Celli and Fiocca, and others 

 — that the amoebae cultivated from stools were identical with the 

 dysentery amoeba : and it has been maintained by Musgrave and Clegg 

 (1904) and more recent workers apparently for a similar reason. It is 

 true that the small free-living amoebae can only be cultivated together 

 with bacteria ; but this, of course, is because these micro-organisms 

 form the food upon which such amoebae live. There is here no question 

 of a " symbiosis," in the proper sense of the word. Moreover, there is 

 no evidence whatsoever that E. histolytica depends for its existence 

 upon bacteria of any sort. It does not eat bacteria, like the free-living 

 amoebae, and no concrete evidence has ever been brought forward to 

 show that it lives in symbiosis — properly so called — with any other 

 organism. t The hypothesis at present adds an unnecessary complica- 

 tion to the life-history of the parasite, and is not worth discussion until 

 some facts can be produced in its favour. 



Pathogenesis. — Only since the publication of the admirable work of 

 Walker (191 1, 1913), has the relation ot E. histolytica to man been 

 correctly understood. All the more recent work — including the vast 

 experience gained during the War — has abundantly confirmed his con- 

 clusions.! It is thus possible, I believe, to deal now with these, and 

 their consequences, as facts ; and to give them here with that brevity 

 which certain knowledge alone will permit. 



E. histolytica, although a tissue parasite, does not usually cause 

 dysentery or any other clinical symptoms in its host. As it destroys the 

 tissues, these regenerate, and the parasite and its host live in a state 



* Schaudinn appears to have taken this notion from Jiirgens (1902). It has found 

 favour also with Craig and othets. 



t The suggestion that attacks of amoebic dysentery are due to some unexplained 

 co-ordinated action between E. histolytica and certain unknown bacteria, appears to 

 be equally unfounded. The idea has been frequently expressed, however, since the 

 time of Janowski (1897), though on what grounds I am unable to discover. It originated, 

 I believe, through a confusion of amoebic with bacillary dysentery. 



X The important work of Wenyon and O'Connor (1917) requires special mention in 

 this connexion. 



