Theory of Peftilential Fluids. , i89 
it is obferved, that although the city of Lifbon is one of the 
filthieft in Europe, and the moft infefted with putrid effluvia, 
yet that it neverthelefs is remarkable for its falubrity., This 
is attributed by Mr. Da Cofta to the calcareous materials, 
of which the buildings and pavements are conflructed, ab- 
forbing and neutralifing the feptic fluids, the caufe, accord- 
ing to Dr. Mitchill’s theory, of all contagion. 
In reply to this I would obferve, that from the author’s 
own account it is evident that the calcareous earth in the 
city of Lifbon does mot deltroy the putrid exhalations in any 
fenfible degree, and therefore cannot prevent any diforders 
to which they may give rife. The houfes, he obferves, are 
very offenfive, from the privies, and from inattention to clean- 
linefs. The mouths of the fewers go to. the wharves, and are 
bare at low water. The fluid which comes from thefe con- 
tains fo many infectious matters that its /lrong putrid fmell 
can fearcely be endured! It is plain, therefore, that the pu- 
trid exhalations are not deftroyed, or, at Jeaft, that they are 
fo quickly generated as to annoy the olfactory fenfe in an 
intolerable degree. The bodies of the inhabitants are con- 
tantly immerfed in putrid exhalations, yet contagion is not 
produced. The inference is, that putrid exhalations are not 
its immediate caufe. Contagion arifes where no putrefac- 
tion is going on, at leaft in any degree perceptible to the 
fenfes; as when a number of perfons are crowded together 
in jails, and even in the houfes of the poor in the winter 
feafon, without fufficient ventilation. On the other hand, 
putrefa&tion may be prefent, in a very high degree, without 
giving birth to contagion, as may be obterved in flaughter- 
houfes, cat-gut manufactories, &e. 
But, is it proved fufficiently that calcareous matters do 
abforb and neutralife feptic exhalations? Mr, Da Cofta re- 
marks, that he has obferved, two or three times, in Lifbon, 
dead animals upon the ruins of houfes, and of courfe fur- 
rounded by calcareous earth, in a ftate of deficcation ;. and, 
at the fame time, two or three fathoms diftant, another ani- 
mal dead too, and lying upon another kind of foil, in a ftate 
of complete putrefaction. I do not prefume to. queftion the 
truth of this, fince it was a matter obvious to the fenfes: but 
I deny 
