Ethel M. Elderton and Karl Pearson 
569 
(c) The attack-rate appears to be greater in the more prosperous towns and 
in towns of somewhat better sanitary conditions. We have not found the pre- 
valence of diphtheria associated with overcrowding or with the conditions leading 
to high infant mortality. 
(d) While a low birthrate, taken either as a measure of prosperity, or as 
a measure of the employment of women and so of the prevalence of hand feeding, 
appears to have no significance for the attack-rate of diphtheria, smoke-producing 
manufactures are probably unfavourable to the prevalence of the disease, which 
appears to attach itself in the main to the large ports and metropolitan suburban 
districts. 
(e) The association between the attack- and isolation-rates observed is not 
very significant, and while it might, to a very small extent, be due to increased 
isolation following or accompanying increased attack, it is more probably an 
association due to the more prosperous towns practising more isolation, and also 
to there being some element in prosperity which assists the spread of the disease. 
Generally all the correlations are of a low order; they contain, however, 
nothing to support the theory that isolation markedly limits the incidence of 
diphtheria ; the disease itself does not appear where overcrowding is greatest nor 
where the population is most dense ; on the other hand isolation is most practised 
in those towns where domestic servants are most common and which may be 
supposed to be most prosperous. The chief argument for isolation — which can he 
drawn from the present data — is a lessened case-mortality, but such mortality 
might be obtained in all probability by specialised medical service as apart from 
isolation. 
