THE PRESENT STATE OF KNOWLEDGE OF THE AMOEBAE 13 



a series of carefully planned and executed experiments on human beings. 

 This work finally solved all the chief problems connected with the 

 relation of amoebae to dysentery. It confirmed and vastly extended 

 the earlier observations of the Italian workers, of Quincke and Koos, 

 and of others, and placed our knowledge of the subject on a firm 

 foundation of fact which is still unshaken and probably unshakable. 



There are, however, certain minor details in which Walker's 

 conclusions must now be qualified. His statement that the free-living 

 amoebae belong to the genus Amoeba is incorrect. The forms which he 

 studied — the so-called " Umax amoebae " — certainly do not belong to 

 the genus Entamoeba ; but it is equally certain that they do not belong 

 to the genus Amoeba Ehrenberg, but to other genera. Further, it is now 

 certain that there are not merely two intestinal Entamoebae in man. 

 There are, as later work has shown conclusively, at least five different 

 species belong to four distinct genera. Of these, however, only one — 

 E. histolytica — is pathogenic, as Walker maintained. 



Apart from these later additions to our knowledge, there is little to 

 be changed in Walker's conclusions. His work is, and will probably 

 remain, one of the most brilliant contributions ever made to medical 

 zoology. For my own part, I regard the chief problems connected with 

 the relation of intestinal amoebae to dysentery and other diseases as 

 solved finally by Walker's work. The researches of later workers are, 

 if read in the light of his results, all easily comprehensible and confirma- 

 tory. Among these workers Wenyon, Darling, and James, must be 

 specially mentioned, on account of the important additions which they 

 have made to our knowledge : but their work will be considered in 

 greater detail later. 



From time to time writers have since relapsed into the old mistakes ; 

 but it is clear that this has always been due to ignorance of the facts or 

 failure to understand the knowledge already acquired. In recent years, 

 for example, Gauducheau (1915) has questioned the correctness of 

 Walker's conclusions — but without understanding them, and from the 

 standpoint of the early days of confusion. Again, Knowles and Cole 

 (1917) have counselled us to go back to the same period, by attempting 

 to show that all the intestinal amoebae of man belong to one species. 

 Their proposal to call this hypothetical " species " by the inadmissible 

 name of " Entamoeba coli communis " shows how little qualified they are 

 to express any opinion on questions of protozoology, biological 

 systematics, and nomenclature. Many other recent workers have not 

 only been unable — on account of their imperfect zoological knowledge 

 — to distinguish different genera and species from one another, but tiiey 

 still continue to confuse these organisms with cells belonging to the 

 human body. The recent works of Bartlett (1917) and Thomson and 

 Thomson (1916a) supply instances of this: but the just criticisms of 

 Bahr and Willmore (1918) fortunately make it superfluous to discuss 

 these observations further. Thomson and Thomson (1916) have even 

 published work undertaken to ascertain whether the dysentery amoeba 

 fives in the sand in Egypt. Their views, apparently, are closely similar 

 to those of some of the earliest workers, and their standpoint is that of 

 Musgrave and Clegg, — which has really been untenable since the days 

 of Casagrandi and Barbagallo, and inexcusable since the work of Walker 

 and Sellards. Many other recent mistakes could easily be cited : but as 

 they all rest upon a similar ignorance of facts which are no longer even 



