[3] In 1551 he was attending in Shrewsbury when a notable outbreak of sweating sickness occurred in the town; the following year, after his return to London, he published A Boke or Counseill Against the Disease Commonly Called the Sweate, or Sweatyng Sicknesse (1552), which became the main source of knowledge of this disease, now understood to be influenza.

[citation needed] He was elected nine times president of the College of Physicians, an account of which, Annales collegii medicorum 1520-1565, he left in manuscript.

He returned to Cambridge from London for a few days in June 1573, about a month before his death, and resigned the mastership to Thomas Legge, a tutor at Jesus College.

He died at his London house, in St Bartholomew's Hospital, on 29 July 1573, but his body was brought to Cambridge, and buried in the chapel under the monument which he had designed.

In 1564, he obtained a grant for Gonville and Caius College to take the bodies of two malefactors annually for dissection; he was thus an important pioneer in advancing the science of anatomy.

[3] Caius was also a pioneer naturalist, prepared to make his own observations about nature rather than simply relying on accepted authorities.