arresting the progress of murrains among cattle by a separation of
the diseased from the healthy. Their herds alone enjoyed that
protection which they held it impracticable to extend to human
society, because they had no wish to do so. That the governments
in the fourteenth century were not yet so far advanced as to put
into practice general regulations for checking the plague needs no
especial proof. Physicians could, therefore, only advise public
purifications of the air by means of large fires, as had often
been practised in ancient times; and they were obliged to leave it
to individual families either to seek safety in flight, or to shut
themselves up in their dwellings, a method which answers in common
plagues, but which here afforded no complete security, because
such was the fury of the disease when it was at its height, that
the atmosphere of whole cities was penetrated by the infection.

Of the astral influence which was considered to have originated
the "Great Mortality," physicians and learned men were as
completely convinced as of the fact of its reality. A grand
conjunction of the three superior planets, Saturn, Jupiter, and
Mars, in the sign of Aquarius, which took place, according to Guy
de Chauliac, on the 24th of March, 1345, was generally received as
its principal cause. In fixing the day, this physician, who was
deeply versed in astrology, did not agree with others; whereupon
there arose various disputations, of weight in that age, but of
none in ours. People, however, agree in this--that conjunctions
of the planets infallibly prognosticated great events; great
revolutions of kingdoms, new prophets, destructive plagues, and
other occurrences which bring distress and horror on mankind. No
medical author of the fourteenth and fifteenth centuries omits an
opportunity of representing them as among the general prognostics