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105
and less likely to convey it to another. (f) The increased general
recognition, during the last 10 or 20 years especially, of contagion
as the source of certain diseases, and increased knowledge of the
means of avoiding its spread, may be recognised as a sanitary
improvement of no slight value. It is obvious that these sanitary
changes are not calculated to effect even all zymotic diseases in
the same manner and to the same extent. The chief fevers are
(1) Malarial Fevers, (2) Typhus, (3) Typhoid. There is much uncertainty
concerning the fever classed as " simple continued," nor
does this appear ever to have contributed largely to the returns.
Now, Malarial Fevers are directly dependent on the development
of the contagia in swamps and marshes; when these are
adequately drained the fevers disappear. Typhus Fever, which
seems to have furnished the largest share of "fevers" in the last
and in the beginning of this century, is found to prevail in connection
with overcrowding in dark ill-ventilated dwellings, combined
with deficient nutrition. When these conditions cease, the
fever disappears, and Typhus has thus become almost unknown
in this country at the present day. Typhoid Fever is directly
dependent on the contagia furnished by the excreta of one case
being introduced into the alimentary canal. Where, by means of
adequate drainage and personal cleanliness, this is prevented, the
disease is prevented also. In the case of each of these fevers,
then, there are special circumstances developing the disease which
sanitary improvements tend directly to remove. There is no like
feature in the case of Small-Pox. It resembles Measles in this,
that the spread of it is not connected with any particular sanitary
fault, as distinguished from those general conditions which tend
to the spread of infectious disease. There is no evidence in the
history of Small-Pox, either before or during the nineteenth
century, to connect outbreaks of that disease in a special way
either with imperfect removal of excreta, or with lack of air and
light, or with deficient food, or with lack of personal cleanliness.
Moreover, the general tendency of sanitation to lower the
prevalence and the fatality of the disease is largely neutralised
both in the case of Small-Pox and Measles by the greater facility