acquired in England, the manner in which he became infected 

 is, as in the other cases just mentioned, still uncertain. 



At this time it was generally recognized that carriers of 

 S. histolytica are by no means rare in the tropics, and probably 

 also in sub-tropical countries. That many soldiers returning from 

 tke Near Eastern theatres of war were infected with the parasite 

 had been shown conclusively : and as H. histolytica was not 

 known to occur in the normal civil population of Great Britain, 

 it seemed natural to suppose that the returning carriers con- 

 stituted the source from which were derived the few known 

 cases of infection undoubtedly acquired in this country. A very 

 important point, however, which made one hesitate to accept this 

 conclusion unreservedly was this : M histolytica was known to be 

 disseminated in the same way as the other protozoa of the human 

 bowel — the harmless amoebae and flagellates. These we knew to 

 occur in persons who had never left the British Isles. Why, 

 then, should not U. histolytica, if once introduced into this 

 country, spread through the population in precisely the same 

 manner? That there had been abundant opportunity for its 

 introduction in the past could hardly be doubted: and consider- 

 ing this question in all its bearings, I soon came to the conclusion 

 that it would be somewhat remarkable — to say the least — if 

 E. histolytica were absent, at the present time, in the native 

 British population. Against this supposition, however, was the 

 fact that typical amoebic diseases — dysentery and liver abscess — 

 appeared to be extremely rare in this country. Yet this objection 

 might not be very cogent : for we were beginning to realize that 

 amoebic diseases are not very common even iii countries where 

 E. histolytica is notoriously endemic, and that carriers of the 

 parasite, displaying no clinical symptoms of infection, are far 

 commoner than was originally supposed. We knew at that time, 

 with a fair degree of certainty, that the dysenteric. convalescents 

 reaching this country from abroad were heavily infected with 

 E. histolytica : but we also knew — or were beginning to know — 

 that the dj'sentery from which these patients had suffered in the 

 field was, in most cases, not amoebic but bacillary. From reliable 

 observations made on the spot it seemed certain that less than 

 10 per cent, of the dysentery in the armies abroad was due to 

 E. histolytica ; whereas in the same troops, when they reached 

 England, twice or thrice this percentage were found to be carriers 

 of the parasite. 



Another fact also came to light in the winter of 1916-17. 

 Soldiers returning to England from the French front, many of 

 them men who had never at any time been in any countries save 

 England and France, were also found to be infected to a consider- 

 able extent with E. histolytica. Mr. Redman King, at Barton 

 Dysentery Ddpot, investigated a number of such cases ; and in 

 a series of 1,300 convalescent dysenteric patients, whom I 

 examined at this time at the Manor War Hospital, Epsom, I found ^ 



' See Dbbell, Gettings, Jepps, and Stephens (1918). 



