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six "Orders." The first and second Orders, ("Miasmatic"
and "Diarrhoeal"), include the diseases which the RegistrarGeneral
calls "the seven principal diseases of the zymotic
class," still grouping under the generic term "Fever" the
three distinct fevers, "Typhus," "Enteric," and "Simple
continued." These "seven" diseases have a high interest
for sanitarians, arising out of their more or less preventible
character; it being customary, moreover, to regard the
absence or the prevalence of them, as the case may be, as a
test of the sanitary condition of a district. But, without
under-rating the importance of this test, there are limitations
to its applicability which must be borne in mind if we
would draw sound conclusions. What I mean may be best
explained by an illustration or two founded on our own local
experiences within the last few years. Thus Measles was
very fatal in 1874 and 1876; the deaths were far above the
average; it was the zymotic disease that gave a special
character to those years. In 1875 and 1877, on the other
hand, the deaths from Measles were below the average; but
the lower mortality—evidence of the diminished prevalence
of the disease—was due to the excessive prevalence
and fatality of the malady in the preceding years. In saying
this, I do not, of course, ignore the fact that one epidemic
of a zymotic disease may be more severe than another ; still
less am I forgetful of the fact that the fatality of an epidemic
is largely influenced by the measures taken, or the neglect
to take measures, for limiting the spread of infection.
Again; the rate of mortality in the Metropolis from
whooping cough in 1881 was the lowest on record; it is not
surprising to find, therefore, that in 1882 the disease was
excessively fatal.
Diarrhcea may be cited as an illustration of quite
another kind. The mortality from this disease amongst
infants was excessive in 1878; the mortality in 1879 was
much below the average; but the diminished mortality in the
second year had no relation to the excessive mortality in the