From these things he must proceed to investigate everything else.
For if one knows all these things well, or at least the greater part
of them, he cannot miss knowing, when he comes into a strange city,
either the diseases peculiar to the place, or the particular nature
of common diseases, so that he will not be in doubt as to the treatment
of the diseases, or commit mistakes, as is likely to be the case provided
one had not previously considered these matters. And in particular,
as the season and the year advances, he can tell what epidemic diseases
will attack the city, either in summer or in winter, and what each
individual will be in danger of experiencing from the change of regimen.
For knowing the changes of the seasons, the risings and settings of
the stars, how each of them takes place, he will be able to know beforehand
what sort of a year is going to ensue. Having made these investigations,
and knowing beforehand the seasons, such a one must be acquainted
with each particular, and must succeed in the preservation of health,
and be by no means unsuccessful in the practice of his art. And if
it shall be thought that these things belong rather to meteorology,
it will be admitted, on second thoughts, that astronomy contributes
not a little, but a very great deal, indeed, to medicine. For with
the seasons the digestive organs of men undergo a change.