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11
During the nine years 1892 to 1900 more deaths were due to diarrhoea
than to any other of the principal zymotic diseases. This is seen in the
following table :—

It has been proved that the temperature of the earth is one of the
most important factors concerned in the development of summer
diarrhoea, and that the summer rise of diarrhceal mortality does not
commence until the mean temperature recorded by the four-foot earth
thermometer has attained somewhere about 56 degrees Fahrenheit.
This subject of summer diarrhoea has been dealt with by me in the
Milroy Lectures, delivered before the Royal College of Physicians of
London. The main facts of the disease are that—
1.—It is for the most part a disease of towns.
2.—It chiefly affects children.
3.—It prevails in the third quarter of the year.
4.—It is spread only rarely by infection from the sick to the
healthy.
5.— It increases in hot and dry, and lessens in wet summers.
These strongly marked features would have to be accounted for by
any theory capable of serious consideration. After a careful investigation
of the matter, I have come to the conclusion that epidemic diarrhoea is
due to the organic pollution of street dust by horse-dung. Many bacteria
are common inhabitants of the intestine both of the horse and of man ;
they are deposited in the streets in enormous numbers, and when dry
are blown about in the form of dust. In this way town houses and
larders, milk shops, restaurants, and other places where food is stored or
consumed are exposed to contamination by numerous kinds of microbes,