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43
44. The Annual Report for 1905 contained a special
report on a statistical investigation into school incidence
of scarlet fever and diphtheria during the ten years 18961905.
45. In the 1910 Annual Report I described an investigation
into the incubation period of scarlet fever. The result was
to show: (1) That the period of incubation varies from one
day to six months; (2) That it is barely the majority of the
total cases in which incubation is under seven days (3) That
in a considerable proportion of cases it is over four weeks;
and (4) That the days from the second to the. fifth after
exposure are those in which most secondary cases occur.
DIPHTHERIA.
46. 244 cases of diphtheria were notified (excluding 77
cases of mistaken diagnosis), compared with 147, 204, and
381, in the three preceding years. The case-rate (number of
cases per 1,000 population), corrected for cases of mistaken
diagnosis was 1.91, compared with 1.15, 1.68, and 3.09, in
the three preceding years, and 2.13, the average of the
ten preceding years. 4 of the cases were bacteriological,
i.e., had no symptoms.
47. There were 17 deaths, compared with 5, 11, and 20,
in the three preceding years. The death-rate was 0.13,
compared with 0.16 in 1912, 0.09 in 1911, and with 0.14
the average of the five preceding years. The London deathrate
was 0.09, compared with 0.10 in 1912, 0.14 in 1911,
and 0.14 in the five preceding years.