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14
kill directly if very concentrated. In a less degree of
concentration these poisons frequently produce fever,
diarrhoea, scrofula. If still further diluted, they may
become innocuous, or, at least, their effects may escape
detection. Now dilution depends on two processes:
first, the carrying off a portion of the poison into the
general body of the atmosphere; secondly, the mixing
what remains with as large a quantity of fresh air as
possible. Both these processes are effected by providing
windows in two aspects of a house, so that from whichever
side the wind may blow, a current shall be established.
Whilst upon this subject, I wish to urge a
consideration very much overlooked by hyper-scientific
ventilaters. Along with fresh air, it is of vital importance
to afford access for light. The chemical action
of light is a most essential means of purification. I have,
therefore, in every case that admitted it, recommended
the piercing a window of sufficient size at the highest
point of the stair-case, or in the back wall of the upper
room. By this means we attain the greatest amount of
benefit, by supplying air of the purest quality, because
it is drawn from strata more removed from the terrestrial
sources of contamination, and more exposed to the
purifying influences of currents, light, and heat.
I have the honour to be,
Gentlemen,
Your faithful Servant,
ROBERT BARNES, M.D.
13, Devonshire Square,
18th July, 1857.