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birth-rate of the most favoured classes, to the extensive immigration into the
country of large numbers of less favoured people, and to the other items that show
that the inherent capacity of the population may not have improved. It would
seem, therefore, that if the tuberculosis death.rate has declined in the United
States, it has not done so because of the improvement of stock during the period
under question, but rather in spite of it.
"On the other hand, the facts in both parts of the world are not at all inconsistent
with the assumption that we are concerned with changes in the environment
of the individuals whom we are considering. . . . From every angle, there is good
evidence that the population of America is better off. Never before in the history
of the country has so favourable a change come over the environment of the people
as in the years subsequent to the great war.
"May we not, therefore, conclude that the very nature of the disease as
expressed in its differential incidence in the various groups of the population and
in its capacity to change, is more consistent with the first than with the second
of the two explanations ? " . . . .
Dr. Dublin does not omit to record the facts that the high rates in California
and Colorado " are due in large measure to the immigration of tuberculous persons
to those areas " (p. 8); and, again, that the high rates in Denver and San Antonio
" reflect the concentration of migrant tuberculosis within their limits." His remarks
too, upon the effect upon the immigrant from the rural parts of Ireland of life in
crowded American cities are well deserving of note.
In the diagram on p. 22 the deaths in four.weekly periods are shown annually influenza,
in and since 1890 from diseases of the circulatory system, pneumonia, bronchitis,
and influenza, and also the average temperature.
There is a close relationship between the winter temperature and the deaths
from diseases of the circulatory system, a sharp peak in the mortality curve being
associated with a period of winter temperature below the average; but there are
it will be noticed occasions when the peak in the mortality curve is greater than
can be accounted for by temperature changes, and the cause of this supplementary
peak is seen on reference to the contour of influenza mortality, an increase in the
number of deaths certified as due to heart disease being invariably found during
epidemics of influenza.
The effect of periods of cold weather in the winter is also clearly shown in the
curves of mortality from pneumonia and bronchitis, and in both there are again
found peaks associated with influenza epidemics, independent of any conspicuous
temperature changes. In the case of bronchitis, the mortality is much higher in
the earlier years shown than in more recent years, even including the year of the
great influenza pandemic—.1918: the reason for this appears to be in part, that in
the earlier years there were several winters of exceptional severity, and partly that
some change in the practice with regard to certification has occurred during the
interval of time separating the two series of influenza pandemics.
The behaviour of diseases of the influenzal group during 1923 was watched with
close attention. The immediately preceding prevalence of " influenza," that of
the early weeks of 1922, caused a maximum mortality (551) in the second week of
that year. There followed later a very small recorded increase in the deaths,
attaining a maximum figure (56) in the 14th week of 1923. It was not, however,
until the autumn of the year that it became strikingly apparent " influenza " was
again afoot, and the recent prevalence attained a maximum mortality (178) in the 7th
week of 1924. It was a few weeks later followed by an increase in the notifications
from encephalitis lethargica, which attained a maximum in the 18th week of 1924.
Truly, during the last two years at any rate, influenza in one or more of its phases
has been endemic in London. The occasion seems a fitting one for a few words of
comment on this phenomenon of the endemicity of influenza.
Hirsch, in presenting his "Chronological Survey of Epidemics of Influenza,