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other than those chemically identified—stinking gaseous products 
of organic decomposition, which force themselves upon popular 
attention: A popular authority, writing upon this point, says: 
“Exposure to the sufficiently concentrated fumes of organic 
decomposition (as for instance in an unventilated old cesspool, or 
long-blocked sewer), may, no doubt, prove immediately fatal, by 
reason of some large quantity of sulphide of ammonium, or other like 
poisonous or foetid gas, which the sufferer suddenly inhales ; and 
far smaller doses of these foetid gases, as breathed with extreme 
dilution in ordinary stinking atmospheres, both give immediate 
headache and general discomfort to sensitive persons temporarily 
exposed to them, and also appear to keep in a somewhat vaguely 
depressed state of health, many who habitually breathe them.” 
Upon these points I am able to speak from painful experience. 
After having been temporarily exposed to an insanitary locality in 
the course of my inspection, however much the impure gases may 
be impregnated with ozone, I almost invariably suffer daily for 
some time from diarrhoea, and a depressed state of health. People 
of a sensitive temperament are most susceptible to the influence of 
these impurities, and much more likely to be attacked by them 
than those of an opposite nature. The same thing will apply 
equally to infective water as to infective air. In the former, just 
as in the latter, the zymotic malignity is but indirectly and most 
imperfectly suggested to us by qualities which strike the common 
sense, or by matters which chemical analysis can specify. As the 
sense of smell possessed by man, will cause him to turn away with 
disgust from certain emanations, so will it, and common taste and 
sight, cause him to be repelled by certain waters. As the chemist can 
show certain foulness in the one, so also can he show certain foulness 
in the other. People under the influence of filth, suffer not only 
from that influence, but also from other removable causes of disease ; 
and, in endeavouring to estimate exactly the injury which is derived 
from filth, those additional influences should, as far as practicable, 
be matter of separate account. On one hand a filthy neighbour- 
hood may be so poor, that mere privation is an appreciable cause 
of disease in it, On the other, the population may be so badly 
a 
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