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The rise in the Diarrhoea death rate does not begin until the average weekly
temperature of the earth thermometer (suspended in an iron tube 4 feet deep) has
attained 56 degs. Fahrenheit, or thereabouts. This takes place about a week later
than in the atmosphere. Allowing that death occurs in a week to a fortnight after
the onset of the disease, this relationship is observed in the following table, which
gives the deaths from diarrhoea for the last three years. The years 1911, 1912 and
1913 differed materially in the matter of rainfall, heat and sunshine.
In 1911, the mean reading of the thermometer was above the week's average in
the 65 years ended 1905, during the 18 weeks from the beginning of July to the end
of the first week in November, with the exception of three weeks, one being equal
to the week's average.
In 1912 it was below the average, with the exception of 5 weeks, these being
the last three weeks in July, third week in October, and the first week in November.
It was below the average in every week during the corresponding period in 1913,
with the exception of 7 weeks. It was above the average during the last week in
August and from the last week in September onwards it remained above the
average.
The summer and autumn of 1911 were dry and hot, and the death rate from
diarrhoea was very high.
The summer and autumn of 1912 were wet and cold, and the deaths from
diarrhoea were about two-thirds less than in the previous year. At the end of the
third week of August there had been 180 deaths from diarrhoea of children under
two years of age in 1911, 30 in 1912, and 44 in 1913.
During the first three weeks in August the mean temperature was higher in
1912 than in 1913, but from the beginning of the fourth week until the last week
in September it was higher in 1913.
The rainfall in September was greater in 1913 than in the corresponding month
of the previous year.
In September, 1913, there were 79 deaths of children under 2 years of age from
diarrhoea, as compared with 29 in 1912.
During the months of October and November the mean temperature was
higher in 1913 than in 1912, and, with the exception of two weeks, the temperature
was even higher than in 1911. The rainfall, however, was greater in 1911 than in
1913, and least of all in 1912. During the months of October and November there
were 69 deaths of children under 2 years of age in 1913, 19 in 1912, and 30 in 1911.
It appears, therefore, that rainfall, apart from high temperature, has no influence
on the mortality from diarrhoea, and that the increased mortality is due to the
heat rather than to the deficiency of rainfall.