er. They appear to me
to contain many new, curious, and valuable observations; but one of the
_conclusions_, which he draws from his experiments, I am satisfied, from
my own observations, is ill founded, and from the nature of it, must be
dangerous. I mean his maintaining, that there is nothing to be
apprehended from the neighbourhood of putrid marshes.

I was particularly surprised, to meet with such an opinion as this, in a
book inscribed to yourself, who have so clearly explained the great
mischief of such a situation, in your excellent treatise _on the
diseases of the army_. On this account, I have thought it not improper,
to address to you the following observations and experiments, which I
think clearly demonstrate the fallacy of Dr. Alexander's reasoning,
indisputably establish your doctrine, and indeed justify the
apprehensions of all mankind in this case.

I think it probable enough, that putrid matter, as Dr. Alexander has
endeavoured to prove, will preserve other substances from putrefaction;
because, being already saturated with the putrid effluvium, it cannot
readily take any more; but Dr. Alexander was not aware, that air thus
loaded with putrid effluvium is exceedingly noxious when taken into the
lungs. I have lately, however, had an opportunity of fully ascertaining
how very noxious such air is.

Happening to use at Calne, a much larger trough of water, for the
purpose of my experiments, than I had done at Leeds, and not having
fresh water so near at hand as I had there, I neglected to change it,
till it turned black, and became offensive, but by no means to such a
degree, as to deter me from making use of it. In this state of the
water, I observed bubbles of air to rise from it, and especially in one
place, to which some shelves, that I had in it, directed them; and
having set an inverted glass vessel to catch them, in a few days I
collected, a considerable quantity of this air, which issued
spontaneously from the putrid water; and putting nitrous air to it, I
found that no change of colour or diminution ensued, so that it must
have been, in the highest degree, noxious. I repeated the same
experiment several times afterwards, and always with the same result.

After this, I had the curiosity to try how wholesome air would be
affected by this water; when, to my real surprise, I found, that after
only one minute's agitation in it, a candle would not burn in it; and,
after three or four minutes, it was