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each of the eight years since notification commenced, and the rates are
calculated upon the estimated population of each district for each year
according to the censuses of 1891 and 1896. The home district of
Chelsea without Kensal Town has been taken, as the inclusion of
Kensal Town tends to obscure the topographical relations which the
tables indicate.
Contrasting the two tables as regards the behaviour of scarlet
fever and diphtheria amongst a large population, it will be seen that
whilst there are great fluctuations in prevalence of scarlet fever from
year to year in West London, the fluctuations in prevalence of
dip htheria are comparatively limited. There was a steady rise of
diphtheria prevalence from 1891 (15.1 per 10,000) to 1896 (25.5 per
10,000), but the fall has already commenced. Again it will be seen
that in years when scarlet fever prevalence was above the average,
nearly all the parishes suffered in a corresponding degree, and vice versa
when there was but little prevalence. There are, however, some
exceptions to this rule, as for instance: Fulham in 1894, Chelsea in
1895, and Fulham again in 1897 ; these exceptions being probably
dependent upon some locally acting cause, possibly special school
influences. In diphtheria, however, this rule does not apply to nearly
the same extent; and the table shows that of two contiguous parishes
one may have for a succession of years a diphtheria incidence-rate
twice or even three times as great as that of its neighbour. It is
evident that the infection of diphtheria is not so rapidly diffusible or
explosive as that of scarlet fever. As a set-off against this, however,
the table shows that the infection of diphtheria is much more persistent
in a district, where it has once strongly taken root, than is the scarlet
fever contagion. The diphtheria rate tends to remain permanently
high in a district for two, three, four, or more years. This is specially
noticeable in the cases of Fulham, Hammersmith, and Chelsea.