68 



tion — apparently world-wide; by its frequency — a considerable 

 percentage of every race of man properly studied having been 

 found infected ; and by the fact that its normal host is the 

 ' healthy ' carrier. In the course of ages JS. histolytica has become 

 well adapted to man, and man well adapted to E. histolytica. 

 But there are many races of Man, and there are probably manj' 

 races of E. histolytica — ^^some of these, indeed, being already easily 

 recognizable by the dimensions of their cysts. On analogy with 

 other protozoa it is probable that there are also many physio- 

 logically different races — at present indistinguishable. It is 

 therefore by no means an extravagant hypothesis to suppose that, 

 in the course of time, particular races of amoebae have become 

 specially adapted to particular races of human beings. The races 

 of E. histolytica occurring in Britain may well be peculiarly 

 suited to a life in Britons : the races in Africa to African natives. 

 But if the Briton goes to Africa, or if the African comes to 

 Britain, and acquires the parasite indigenous to the country, 

 it is possible that these new combinations might produce a 

 different result. It is possible that African strains of amoebae 

 may be unsuited to a life in British bowels, and may in this 

 abnormal environment give rise to dysentery more readily than 

 they do in theii* native habitation in the negro. I will not 

 assert that this is the correct or complete explanation of what 

 appear at present to be the facts regarding the incidence of 

 amoebic diseases ; but I think that some such hypothesis as the 

 foregoing offers the most plausible line of interpretation, and 

 I know. of no other which is consistent with all the established 

 facts — many of which are very curious and, at first sight, contra- 

 dictory. 



I would emphasize here once more that the observations already 

 made in Britain, in France, in Holland, and in adjacent European 

 countries, all tend to show most clearly that E. histolytica is as 

 much at home in Western Europe as it is in the tropics. The 

 distribution of this amoeba is almost certainly world-wide. It 

 probably occurs now wherever there are men, and has so occurred 

 from time immemorial. E. histolytica,like the eagle of Prometheus, 

 preys upon the perpetually regenerated flesh of the human body; 

 and in the words quoted by ' the beloved Physician ', ' Where- 

 soever the body is, thither will the eagles be gathered together.' 



In conclusion, I will sum up in a few words the present posi- 

 tion with regard to E. histolytica — as I conceive it — in so far as it 

 concerns the population and practitioners of this country. 



Entamoeba histolytica is, or may be, a ' cause ' of human 

 disease ; but usually it is comparatively harmless to the persons it 

 inhabits — at all events, in a population in which it has been long 

 established. The parasite occurs commonly in Britain, in the 

 resident native population, but to the majority of its hosts it 

 causes little or no inconvenience. It is probably not a new or 

 recently imported parasite, but at least as old an inhabitant of 

 these islands as the British nation. It has apparently caused but 

 Jittle trouble in the past, and is not likely to cause more in the 



