"Dog Days" is the name for the most sultry period of summer, from about July 3 to August 11. Named in early times by observers in countries bordering the
Mediterranean, the period extended from 20 days before to
20 days after the conjunction of Sirius, the Dog Star and the sun. In the
latitude of the Mediterranean region this period coincided with hot days that
were plagued with disease and discomfort.
Dog Days were popularly believed to be an evil time "the Sea boiled, the Wine turned sour, Dogs grew mad, and all other creatures became languid; causing to man, among other diseases, burning fevers, hysterics, and phrensies." according to Brady’s 1813 Clavis Calendaria or a Compendious Analysis of the Calendar: illustrated with ecclesiastical, historical, and classical anecdotes.
A must read this summer?