harbours infection and creates the only conditions under which the malady
can appear. For example, during two consecutive winters cerebro-spinal
fever had appeared in barracks capable of housing 2,000 men. A simple and
effective method of ventilation was then introduced. From that day to this
not a single case of cerebro-spinal fever has occurred in these barracks,
although there have been outbreaks of this disease in the town in which the
barracks are situated.

There are many other diseases peculiar to civilisation, and concerning
the wherefore and the why an apposite passage occurs in the works of Sir
William Gull.

"Causes affecting health and shortening life may be inappreciable in
the individual, but sufficiently obvious when their effect is
multiplied a thousandfold. If the conditions of society render us
liable to many diseases, they in return enable us to establish the
general laws of life and health, a knowledge of which soon becomes a
distributive blessing. The cure of individual diseases, whilst we leave
open the dark fountains from which they spring, is to labour like
Sisyphus, and have our work continually returning upon our hands. And,
again, there are diseases over which, directly, we have little or no
control, as if Providence had set them as signs to direct us to wider
fields of inquiry and exertion. Even partial success is often denied,
lest we should rest satisfied with it, and forget the _truer and better
means_ of prevention." [9]

Medical and sanitary science have made great progress in the conquest of
enteric fever, diphtheria, scarlet fever, measles, and whooping cough. The
mortality from bronchitis and from pulmonary tuberculosis has also been
reduced, but nevertheless tuberculosis still claims more victims in the