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45
in some way closely associated with season. Over 90 per cent, of
the deaths occur during the months of July-October.
There is a large increase in the number of deaths compared with
1905, and whatever views may be held as to the causation of
Diarrhœal diseases, there can be no doubt as to the beneficial influence
of an excessive rainfall. The total amount of yearly rainfall
bears no direct relation to the mortality; most of the deaths occur
during the months of July-October, and the factors entering into their
causation would operate most potently during these four months.
1 ne prevalence of Diarrhoea is more closely related to the number
of days upon which rain falls than to the actual amount of rainfall;
it varies almost inversely with the number of rainy days. Though
this ratio does not work out with mathematical accuracy, it is sufficiently
close to warrant the assumption that the relation is one of
cause and effect. The factor may be beyond the control of a sanitary
authority, and probably few would be daring enough to wish for a
wet holiday season, but the manner in which it operates should teach
us something in the prevention of Diarrhœa. The diminished prevalence
is probably not due to the purifying action of rain on the
atmosphere, as in such circumstances the amount of rainfall would
be the determining influence, though it is well known that a heavy
shower in summer has a cleansing effect on the air. It is fortunate
that such is not the mode of action, as nature could not be imitated
in this respect. It is now generally held that the prevalence of
Diarrhoea is dependent on the state of the soil. It is probable that
the micro-organism has its habitat in the superficial layers of the soil,
where, in the form of decaying animal matter, it has its pabulum and
manufactures its poison. Though the theory that the maximum mortality
from Diarrhoea coincides with the temperature of the earth at
different depths is now doubted, very few doubt the intimate association
of the disease and conditions of the soil. If we consider the state
of the streets and backyards, the influence of rainy weather is explained.
Organic matter is constantly being deposited on the streets;
in dry weather this becomes pulverised and carried in the form of
dust into the houses. Rain maintains in a condition of moisture collections
of dust and refuse, which, in a dry state, would be carried
by the wind or other agencies, and deposited in food, more especially
in milk. To prevent dust, the surface of the street must be kept