prominent Humanist and physician whose classic account of the English sweating sickness is considered one of the earliest histories of an epidemic.

After his student days at Cambridge, Caius visited Italy (1539), studying under Montanus and Andreas Vesalius at Padua. Upon returning to London he practiced medicine and served as president of the Royal College of Physicians for several years. In 1557 he expanded his old college (Gonville Hall), named it Gonville and Caius College, endowed it generously, and in 1559 accepted its mastership.

Caius' medical writings are of particular interest, especially his account of the often fatal sweating sickness, which was epidemic in England six times between 1485 and 1578. A Boke or Counseill against the Disease commonly called the Sweate, or Sweatyng Sicknesse (1552) is the main source of knowledge of this disease, which modern investigators think may have been a form of influenza. Caius attributed the cause of the illness to dirt and filth.