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(a), (b) and (c), and too irregularly localised for channel
(d). I he more uncommon and rarer channels of infection
in recorded diphtheria outbreaks were, consequently,
investigated, viz.: (a) ordinary sore throats developing
into diphtheria, (b) infected water supply, and (c) infected
milk supply. Evidence was obtained of ordinary sore
throats being common throughout the districts affected, but
these ordinary sore throats were prevalent, too, in
neighbouring districts, which were not affected with
diphtheria, so that eventually this channel of infection was
abandoned as a definite cause of the outbreak. Finally, the
water and milk supplies came under review, and, in connection
with the former (the water supply), it was decided
that the outbreak was not sufficiently extensively
widespread, that the cases were too irregularly localised,
to warrant the water supply being suspected as the
infecting cause. The milk supply, therefore, was
the only probable source of infection left, after excluding
all the others, and the evidence from all the affected
districts appeared to point to a milk supply, or supplies,
being infected, in some way or other, with the diphtheria
poison. In this connection, however, there were
difficulties that had to be faced at the commencement of
the investigations. Assuming the existence of such an
infected milk supply, or supplies, how was it
(1) That the outbreak was not more sudden in onset.
of a more explosive nature, and more widespread
following the milk-carts generally, in all the districts
sunolied with infected milk, more especially having
regard to the large amount of milk distributed daily
throughout the districts affected;
(2) That the outbreak did not show a more rapid rate
of increase, having regard to the wav in which the
diphtheria bacillus grows and thrives in milk
(especially raw milk) more even at comparatively
low temperatures than at 37 degrees C. (98.6 degrees
F-);
(3) That the incidence of the disease was practically
not upon milk drinkers, being chiefly upon
adults, and not upon children and invalids, who
are, generallv speaking the orincipal milk consumers,
especially children in better (or best) class
houses;
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