46 



individuals came from the South Wales coalfields. Although the 

 series is small this percentage is remarkably high, when it is 

 remembered that the stools were examined only once apiece. It 

 is probably too high to be without significance, and appears to 

 indicate that miners are infected to a greater extent than many 

 other classes of the community : which might, indeed, have been 

 expected, since the localization and spread of some other parasites 

 in mines is already well known. 



The high rate of infection with E. histolytica found among 

 lunatics should also be noted here. At one asylum Matthews and 

 Smith (1919 a) found 9-7 per cent, of the inmates infected, as a 

 result of making only one examination per case. This is a high 

 rate, but not so high as a previously published record for the same 

 asylum appeared to indicate (Yorke, 1918). This series well 

 illustrates the possible errors in small samples. In the fii'st 

 report, when only 46 cases had been examined, no less than 19-5 

 per cent, were found infected with E. histolytica. Later, when 

 307 cases had been studied, this percentage fell to 9-7. At another 

 asylum, where he examined 504 patients (once apiece). Smith 

 (1919) found only 4-2 per cent, infected. Campbell {supra, p. 31) 

 found 2-94 per cent, of ' mental cases ', in a workhouse, infected 

 with E. histolytica — as compared with 2-75 per cent, in a larger 

 series of ' non-mental ' cases in the same institution. Such figures 

 as these do not justify the conclusion that all lunatic asylums are 

 hotbeds of E. histolytica infection. 



In considering the possible correlation oiE. histolytica infection 

 with particular occupations or modes of life, it is important to 

 remember that the parasite occurs in children — even in those of 

 very tender age. When this is borne in mind, and the results of 

 the investigation of several families by Smith and Matthews ^ 

 and Kuenen ^ are also taken into account, it seems clear that the 

 home is no longer negligible as a source of contagion ; and that 

 occupation may, perhaps, be one of the less important of the 

 factors which determine the acquisition of infection with E. 

 histolytica. 



Geographical Distribution. — In the reports already published, 

 and in those now presented in Chapter III, there is some in- 

 formation about the present distribution of E. histolytica in 

 Britain. It is not complete, but it is, in some respects, suggestive. 



Most of the persons in whom E. histolytica has been found 

 have been interrogated regarding their usual place of resi- 

 dence : and this has been recorded. The workers at Liverpool, 

 Birmingham, Bristol, Brighton, Leeds, Sheffield, and Reading, 

 have found most of their infected eases among residents in the 

 districts in which they worked. The fact that not one of these 

 workers failed to find local cases of infection shows that E. histo- 

 lytica probably has a wide distribution. But by no means all 

 the cases examined were habitually resident in the places in 

 which their examination took place. Some of them had left 

 their native towns or villages — to undergo jnilitary training, 



1 See p. 55, i>ifra. = See p. 60. 



