XI. By studying and observing after this fashion
one may foresee most of the consequences of the
changes. One should be especially on one's guard
against the most violent changes of the seasons, and
unless compelled one should neither purge, nor
apply cautery or knife to the bowels, before at least
ten days are past. The following are the four most
violent changes and the most dangerous :--both
solstices, especially the summer solstice, both the
equinoxes, so reckoned, especially the autumnal.
One must also guard against the risings of the stars,
especially of the Dog Star, then of Arcturus, and also
of the setting of the Pleiades. For it is especially
at these times that diseases come to a crisis. Some
prove fatal, some come to an end, all others change
to another form and another constitution.