en it recurred at eleven at night for about a week, and was
then totally destroyed by opium given in very large quantities, after
having been previously for a few days omitted.

7. _Catameniae periodus._ Periods of menstruation. The correspondence of
the periods of the catamenia with those of the moon was treated of in Sect.
XXXII. 6. and can admit of no more doubt, than that the returns of the
tides are governed by lunar influence. But the manner in which this is
produced, is less evident; it has commonly been ascribed to some effect of
the lunar gravitation on the circulating blood, as mentioned in Sect.
XXXII. 6. But it is more analogous to other animal phenomena to suppose
that the lunar gravitation immediately affects the solids by its influx or
stimulus. Which we believe of the fluid element of heat, in which we are
equally immersed; and of the electric fluid, which also surrounds and
pervades us. See Sect. XXXVI. 2. 3.

If the torpor of the uterine veins, which induces the monthly periods of
the catamenia, be governed by the increase of terrene gravitation; that is,
by the deficiency of the counter-influence of solar and lunar gravitation;
why does not it occur most frequently when the terrene gravitation is the
greatest, as about six hours after the new moon, and next to that at about
six hours after the full moon? This question has its difficulty; first, if
the terrene gravitation be greatest about six hours after the new moon, it
must become less and less about the same time every lunar day, till the end
of the first quarter, when it will be the least; it must then increase
daily till the full. After the full the terrene gravitation must again
decrease till the end of the third quarter, when it will again be the
least, and must increase again till the new moon; that is, the solar and
lunar counter-gravitation is greatest, when those luminaries are vertical,
at the new moon, and full moon, and least about six hours afterwards. If it
was known, whether more menstruations occur about six hours after the moon
is in the zenith or nadir; and in the second and fourth quarters of the
moon, than in the first and third; some light would be thrown on this
subject; which must in that respect wait for future observations.

Secondly, if the lunar influence produces a very small degree of
quiescence, suppose of the uterine veins, at first; and if that recurs at
certain periods, as of lunar days, or about 25 hours, even with