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38
DRAINAGE.
marshes, of cesspools, burial-grounds, or slaughterhouses,
would in any important degree be lessened
by the mere mitigation of fœtor in their effluvia.
Offensive as these are, they at least answer the useful
purpose of warning us against the other poisons
with which they are associated.
Let me likewise take the opportunity of correcting
a mis-apprehension, which, by the use of an inappropriate
word, is sometimes shown to exist on
this subject. The agents in question are spoken of
as dis-infectant. As there is no scientific reason
whatever for believing that they in any degree
interfere with the spread of epidemic or infectious
disease, and as an erroneous opinion on this point
may lead to the neglect of measures which are truly
precautionary and useful, I think it well to state
explicitly, for your information, that there is no
evidence of their possessing any other utility, in the
respects under consideration, than simply and singly
that of removing stink from the atmosphere around
them.
For reducing to a minimum the exhalations which
arise from sewers and house-drains, it appears to
me that the following are the essential principles:
First, to render the current through them as rapid
as possible; and above all, by every care for their
form, their junctions, their slope, and their material,
to provide against the occurrence of obstructions
and deposit: Secondly, to employ in their construction,
so far as may be possible, such substancs as