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the first case had been removed to hospital. Of the remaining six
secondary cases, 2 in one house occurred five days after cessation
of isolation of the primary case, and 1 twenty-two days after.
These must be looked on as probably "Home Return Cases,"
i.e., infected by the primary case after the latter was supposed to
be free from infection; the primary cases had been isolated for
five weeks and four weeks respectively. One case, occurring 29
days after isolation, must be considered as due to ineffectual
isolation.
The remaining two secondary cases occurred 13 and 14 days
after commencement of isolation. It cannot be said that these
were due to failure of isolation as it is well known that the
incubation of scarlet fever is, occasionally, as long as three weeks
and longer. It is equally probable that they were infected by the
primary case. (Thirteen cases in 1906 removed to hospital were
followed by secondary cases at intervals of 7 to 23 days after
removal.) It would, however, be reasonable to attribute one of
them to insufficient precautions being taken. It may then be
said that home isolation was followed by two return cases and two
second cases, due to failure of isolation, or two per cent. of failure.
These results are not unfavourable when the shorter duration
and other advantages of home isolation are considered.
43. Other sources of Infection. A probable source of infection
was found in 267 cases. In 118 cases infection was attributed to
other members of the family. Some of these were never notified
and had no distinct symptoms of scarlet fever, but a history of
sore throats made it probable that they had had a slight attack of
this disease.
44. In 42 cases infection was attributed to friends and neighbours,
and in 79 cases to school attendance; in 9 to fellow lodgers;
and in 9 to travelling or visiting hospitals. The number of mild