42 



It is now necessary to consider each intestinal protozoon in 

 greater detail, since there are special points of interest connected 

 with each and these have hitherto been omitted. I shall begin 

 with Entamoeha histolytica, which is the most important, and 

 which must therefore be considered in greatest detail. 



1. Entamoeha histolytica. — It is clear that infections with this 

 protozoon are by no means uncommon in the resident population 

 of Britain. At least one carrier of this parasite has been found 

 by every worker who has taken part in the present investigation. 

 It has been demonstrated that 3-4 per cent, of examined persons 

 who have never been abroad (over 3,000 cases) are infected ; and, 

 as already stated, this probably indicates that some 7 to 10 per 

 cent, of these individuals actually harboured the parasite. 



If it be permissible to generalize from these findings, for a 

 relatively small number of cases, to the population as a whole, 

 then it appears that the people of these islands are infected to 

 a noteworthy extent — an extent, at any rate, which was quite 

 unsuspected until recently. It may, of course, be objected that 

 such generalization is not yet justified. The sample examined is 

 small : it may not be representative. On the other hand, it may 

 be remarked that the sample, though small, is not very small ; 

 and there is no obvious reason why it should not constitute a fair 

 sample — unless it be that it consists mainly of persons belonging 

 to the lower grades of society. It must not be forgotten, however, 

 that among the higher grades it becomes increasingly difficult to 

 find persons who have never been abroad, and who have therefore 

 only been exposed to infection at home. When this is borne in 

 mind, it appears not improbable that the entire population — 

 including all who have and all who have not been abroad — would, 

 if subjected to examination, prove to be even more heavily 

 infected with E. histolytica than the figures here recorded seem 

 to indicate. There seem no good grounds, at all events, for sup- 

 posing that the incidence for the total population is less. 



The first indigenous case of ^. histolytica infection recorded in 

 Britain is probably that of Dickinson (1862), though the diagnosis 

 rests on indirect evidence.^ The case of Saundby and Miller 

 (1909) appears to be the first in which E. histolytica was actually 

 seen,^ and the case described by Wenyon (1916) was apparently 

 the earliest recognized carrier showing cysts in the stools.^ The 

 later oases, described by the Liverpool workers and others, belong 

 almost entirely to this class — more or less healthy persons (carriers) 

 showing no clinical signs of disease due to their infections. 



> See p. 17. 



2 See p. 19. 



' See p. 7. 



