d a faulty reservoir; whereas the case was proved to be
owing to the chemical action of the water on the lead. Water containing
a large quantity of common air and carbonic acid gas, always acts very
sensibly on metallic lead.

Water, which has no sensible action, in its natural state, upon lead,
may acquire the capability of acting on it by heterogeneous matter,
which it may accidentally receive. Numerous instances have shewn that
vegetable matter, such as leaves, falling into leaden cisterns filled
with water, imparted to the water a considerable solvent power of action
on the lead, which, in its natural state it did not possess. Hence the
necessity of keeping leaden cisterns clean; and this is the more
necessary, as their situations expose them to accidental impurities. The
noted saturnine colic of Amsterdam, described by Tronchin, originated
from such a circumstance; as also the case related by Van Swieten,[21]
of a whole family afflicted with the same complaint, from such a
cistern. And it is highly probable that the case of disease recorded by
Dr. Duncan,[22] proceeded more from some foulness in the cistern, than
from the solvent power of the water. In this instance the officers of
the packet boat used water for their drink and cooking out of a leaden
cistern, whilst the sailors used the water taken from the same source,
except that theirs was kept in wooden vessels. The consequence was, that
all the officers were seized with the colic, and all the men continued
healthy.

The carelessness of the bulk of mankind, Dr. Lambe very justly observes,
to these things, "is so great, that to repeat them again and again
cannot be wholly useless."

Although the great majority of persons who daily use water kept in
leaden cisterns receive no sensible injury, yet the apparent salubrity
must be ascribed to the great slowness of its operation, and the
minuteness of the dose taken, the effects of which become modified by
different causes and different constitutions, and according to the
predisposition to diseases inherent in different individuals. The
supposed security of the multitude who use the water with impunity,
amounts to no more than presumption, in favour of any individual, which
may or may not be confirmed by experience.

Independent of the morbid susceptibility of impressions which
distinguish certain habits, there is, besides, much variety in the
original constitution of the human frame, of which we are totally
ign