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Tt should be added that throughout, the 60 years to which the contours in Diagram II. relate
urbanization has steadily proceeded at the expense largely of rural districts and rural occupations; so
that finally the striking contrast between the shapes of the curves for 1861-70 and for 1901-10 shows
remarkable approximation to that presented in the shapes of the curves for rural counties and urban
counties in 1891-1900 reproduced in the Annual Report for 1913 (page 42).
Evidence of tubercular infection is found post mortem in so high a proportion of cases examined
that it is beyond doubt that susceptibility rather than infection is the determining factor in phthisis
mortality, and certain occupations are known to increase the susceptibility to particular diseases. That
occupations such as tin-mining and file-cutting should gradually undermine the natural resistance to
phthisis is no more difficult of explanation, therefore, than that farming on the other hand should
diminish susceptibility; and granted that the phthisis mortality may be thus controlled for periods of
years the resulting variations in the mortality contours can no longer be ascribed to the existence of
different "clinical entities."
There is a general similarity in the age-incidence of phthisis mortality among coal miners in
different counties, and such divergencies as are observed appear to be governed by the varying incidence
of mortality from respiratory diseases, and also from the differing mortality from all causes. Climatic
conditions undoubtedly influence mortality from respiratory diseases, notably bronchitis, and it would
thus be expected that at higher ages, at the point where the phthisis mortality is decreasing, and the
bronchitis mortality rapidly increasing, some confusion between the two might result in an over-statement
of the phthisis mortality at that age. This possibility was discussed in the Annual Report for 1913,
page 43. Dr. Brownlee in considering the high mortality from phthisis in Ireland in 1851 to 18 0
concludes that "the obvious interpretation of the statistics is that at high ages a considerable
amount of bronchitis was classed as phthisis."If this possibility is borne in mind in dealing with
occupational statistics much of the " old age " type of phthisis maj be accounted for.
Dr. Brownlee thinks that his hypothesis of three "clinical entities" may explain his never having
seen any " demonstrable benefit " from tuberculin treatment in Glasgow. The tuberculin, he says,
may have been prepared in London where middle age phthisis is "prevalent," while in Glasgow " there
is little phthisis of the middle age type." The figures upon which he relies are given in Public Health,
March, 1916, and relate to the four years 1909 12, for he says " piior to 1909 no statistics of any value
with regard to phthisis exist for Glasgow and Edinburgh." He citcs in a section headed "Phthisis
in Scotland, 1860-1910," an example of the kind of misunderstanding which has arisen with regard
to the Edinburgh statistics. His Glasgow figures are, it is tine, more recent, but they are not critically
examined with a view to learning how far they may be affected by migration. Further study of these
figures with this consideration in mind would, t! orefore, seem desirable.
Dr. Brownlee concludes with a review of the mortality from phthisis in London since 1631 as
disclosed in the "Bills of Mortality" under the heading "consumption." As compared with the total
deaths, "consumption "claimed an increasing proportion from about the beginning of the 18th century
to its close, the proportion thereafter declining. Dr. Brownlee suggests as the easiest explanation of
the facts " that an epidemic wave of phthisis spread steadily over London in the 18th century, culminated
about 1800 and has since declined." Further investigation of the data is foreshadowed, and this would
seem desirable, for many epidemiological and social factors may have been operative during 200 years
in a way which might tend to disturb the relationship between the total deaths and those classed to
"consumption," even if this heading can be considered to have had the same meaning throughout the
period under review.
The depletion of the vitality of stocks bv the continued withdrawal of the fittest and by in-breeding,
and the invigoration of stocks by cross-breeding, are effects which, presumably, have influenced
the general death-rate as Well as phthisis mortality since the beginning of last century. Some share in
all this may well be assigned to the increasingly greater freedom of movement in the population from
about that time. This factor may have specially affected, too, the changing proportion of " consumption "
to all deaths in London since 1631.
Influenza
Influenza, cerebrospinal fever, poliomyelitis and polioencephalitis (including encephalitis lethargica).
Influenza in pandemic phase has usually given rise to the impression that it is a " new disease."
The pandemic of 1918 was no exception to this rule, and the first spectre raised, that of Botulism, was
only laid to be replaced by so-called encephalitis lethargica or epidemic stupor, and to be followed by
the insubstantial theory of the Spanish origin of influenza. Such phantoms of the imagination could,
perhaps, only have been bodied forth in an age of specialism, for the present epoch clearly has the defects
of its qualities. But epidemiology refuses to stress unduly the " here and now," for it can recognise
no limits to its enquiries save those of the inhabited world and of the historical period. The technique
and newly-acquired knowledge of the specialist can be of but little service in comparing a current epidemic
with earlier prevalences, possibly of a closely related character ; moreover, the critics of epidemiological
methods sometimes fail to appreciate that they are designed for distinguishing epidemics and not
individual cases from one another.
Fourteen years ago in the Milrov Lectures of 1906 the relation of influenza to English sweat and
the accompanying phrenitis, cerebritis, pleuritis, etc., of the 15th and 16th centuries, and to the dengue
of more recent centuries, was discussed and the attempt was made in the light of the facts elicited to
distinguish between the pandemic and the inter-epidemic phases of influenza. Starting from the salient
epidemiological characters common to both influenza and dengue in pandemic phase (sudden onset,
tendency to relapse, establishment of immunity, "posting character," etc.) the attenip' was made to