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106
stead, to .64 in Shoreditch. Diarrhœa is looked upon as a
disease of bacterial origin. The factors favouring its development
are a high atmospheric temperature and deficient rainfall,
the contamination of food, especially milk, from dust, and the
unhealthy conditions prevailing in crowded cities. The exact
relationship existing between these various factors is not however
yet fully known. The effect of season upon the incidence
of the disease depends upon dryness and heat. A hot, dry
summer, such as that which prevailed in 1906, favours the
disease. A cold, wet summer, on the other hand, is unfavourable.
In 1907 the summer was the very reverse of that which
was experienced the previous year, and the effect of the different
meteorological conditions which prevailed is strikingly exemplified
in the mortality figures for 1906 and 1907 respectively.
In 1906 the 4-foot earth thermometer reached 56 degrees F. on
14th June, or much earlier than in 1907. Fifty-six degrees F.
is what is known as the critical earth temperature for diarrhœa,
i.e., the temperature at which the germ which gives rise to
this particular disease begins to multiply. In 1907 the 4-foot
earth thermometer reached the critical temperature at a much
later date, while the atmospheric temperature remained abnormally
low, hence the unfavourable effect on the growth and
multiplication of the organism.
It will be interesting to give the meteorological conditions
prevailing in the summer of 1907. The 4 foot earth thermometer
registered 56° F. in South London on 29th June, rising
to a maximum of 6o° F. on 15th August, shrinking again to
56° on 13th October. Further, the mean monthly air temperatures
were, June 57.8°, July 6o°, August 61.6°, September
58.9°, October, 51.1°.
While it is clear that the meteorological conditions are by
far the most important in their bearing on the incidence and
mortality from epidemic diarrhœa, the insanitary conditions
prevailing in large towns and cities are amongst the contributing
causes. It is a remarkable fact that breast-fed babies
rarely suffer, while on the other hand artificially-fed children
fall easy victims. This is not difficult to understand