2. The spread and decline of the disease is influenced by local
peculiarities and revolutions in atmospheric constitution.
3. It appears probable, that under peculiar local circumstances, it may
have arisen spontaneously, without having been introduced by contagion;
but this invasion must be considered of very rare occurrence.
4. Although transmitted by contagion, a certain distance preserves the
healthy from the contamination of the diseased.
5. The enforcement of a limit of separation must be considered
indispensable in all our sanitary regulations, in the framing of which
great attention must be paid to discriminate between contagion and
infection--two sources of distemper essentially different from each other.
Although these precautions are pointed out by the result of long and
unbiassed experience, they will in all probability be solely applicable to
the plague: for we have every reason to believe that these sanitary
measures will not prove efficient against the invasion of cholera, the
yellow fever, and other diseases, which are by no means proved to be
infectious or contagious. Without entering into the discussion, I feel no
hesitation in giving it, as my decided opinion, that the cholera and
yellow fever are not contagious.