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16
SEVEN PRINCIPAL ZYMOTIC DISEASES.
Amongst the special causes of death we take as first,
from a sanitary point of view, that important class of
diseases to which, amongst others, belong those which
are contagious and infectious, the contagion also of
which is specific for each disease; that is to say, it
passes in some way from those already affected to
others who, though sound, are in all probability in some
way predisposed to receive it, where finding a fit soil,
it grows and multiplies therein, and is again communicated
to others.
It is customary to take the principal and most infectious
diseases of this class, and to calculate what is
called a Zymotic rate upon the deaths. Now, this selection,
which is that adopted by the Registrar-General,
is purely arbitrary, and really includes ten distinct
diseases ; though, as all fevers are grouped under one
general head, and Diarrhoea and Cholera under another,
they are commonly spoken of as the seven principal
Zymotic diseases. Now, this plan is convenient, as by
adopting it a comparison maybe readilymade with other
districts. All the diseases under this head are highly
contagious or infectious, with one exception, and this is
Diarrhoea; but as this disease is very commonly caused
by bad sanitary conditions, and is indeed, under certain
circumstances, also infectious, it is advisable to retain it.
The first six of these diseases occur, as a rule, once
only during a life time, the incidence of the disease
seeming to exhaust the capability of the individual to