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48
it will be seen that during 1906 and 1907, 1,113 persons were at
risk, and that of these 415 were under fourteen, and therefore at
special risk; whereas, in diphtheria, 571 were at risk and 281 at
special risk.
Therefore, the number at risk includes all those members of
infected homes who had not suffered from the disease at the time of
inquiry, and the number at special risk is a similar statement confined
to those under 14 years of age; and I should add that whereas
the enquiry-forms relating to the subsequent cases suggest in a few
cases a school-origin of infection, and in others the infection is
ascribed to the return of a case from a fever hospital, I have made
no deductions for what are only, after all, surmises, which, moreover,
form a similar proportion to the total in both years. It is impossible
in practice to eliminate all the possible outside causes of infection,
and to say in any case that the subsequent infection of a member of
a family, of whom one had previously suffered from infection, is
due to the failure of the disinfection practiced. Nor can the nonoccurrence
of subsequent infection be taken as an absolutely final
test of the efficiency of disinfection; we have to recognise that the
consequences of inefficiency will depend upon the nature of the
infection, the probability of its retention, the nature of the subsequent
exposure by different individuals, and upon the degree of their
then susceptibility, and it must be borne in mind that often the
most susceptible material at the time is exhausted in the home by
the primary outbreak of infection. Under the ordinary conditions
of home life, at least among the poorer classes, it is barely conceivable
that, when infection occurs, any member of the family escapes exposure
to either the original source of the infection or to the infection given
off by the infected member prior to removal to hospital; but owing
to subtle circumstances that determine immunity the majority escape.
But there can be no reasonable doubt that if A uses a spray
method and B a fumigation method, if A's method is superior in its