64 



who had never been abroad. We know that the parasite occurs 

 in widely separated parts of the country, and is comparatively 

 common. "We know that it occurs at the present time in every 

 part of the world where it has been sought; and from its re- 

 lative harmlessness to human beings it seems probable that its 

 association with mankind is no new thing. The very fact that 

 E. histolytica is now comparatively common in persons who have 

 never left the country, whilst amoebic diseases are uncommon, 

 argues a degree of tolerance in the community such as is incon- 

 sistent with the supposition of its recent importation. Finally, 

 it has not been possible, in those qases where careful inquiries 

 have been made, to establish any direct connexion between the 

 native cases of infection and carriers returning from abroad. 



The proof that E. histolytica and other intestinal protozoa 

 occur not uncommonly in the resident civil population of these 

 islands offers a wide and somewhat novel prospect for con- 

 templation by the British physician. The organisms themselves 

 are — save to those who have studied tropical medicine — 

 comparatively unfamiliar, and consequently apt to be regarded 

 with suspicion. Medical practitioners in this country will there- 

 fore desire some further information concerning the protozoa in 

 question, and will naturally ask what all the figures in this 

 Report really mean — whether they have any practical importance, 

 and, if so, what it is. To answer such questions finally is hardly 

 possible at the present moment. Nevertheless, approximate 

 answers can, I think, even now be found ; and in the remainder 

 of this chapter I propose to give my own general conclusions 

 from the findings before us, and to discuss very briefly certain 

 problems and points of interest which they suggest. 



In the first place, the figures mean — and to my mind this 

 is their worst meaning — that the inhabitants of Britain must 

 frequently consume food and drink which has been exposed to 

 gross contamination with fresh human faeces. The findings 

 demonstrate this conclusively. Of the protozoa here considered, 

 not one lives — so far as we know at present — anywhere but in 

 the human bowel. The cysts of all are discharged in human 

 faeces only; they cannot long survive outside the human body; 

 and they cannot withstand drying. Infection can only be acquired, 

 in natural conditions, by swallowing fresh, undried cysts derived 

 from the faeces of a human being. Consequently, when we find 

 persons infected with intestinal protozoa we must conclude that 

 they have previously swallov/ed particles of the fairly fresh and 

 damp excrement of other persons ; and when we find many people 

 presenting such evidence of pollution, we can only conclude that 

 the disposal of human faeces has not yet been brought generally 

 to that pitch of perfection which seems desirable. 



The exact mechanism by which jEJ. histolytica and other intestinal 

 protozoa are spread through the community is not yet fully under- 

 stood ; but from the facts now available it is clear that in the past 

 we have been too prone to lay stress upon foreign sources of 

 infection. We have ignored the fact that we ourselves harbour, 



