Two aspects of Wren's interest in the biomedical sciences – his experiments on intravenous injection and his collaboration with Thomas Willis on the anatomy of the brain – are already well known. Their particular fame is explained by subsequent developments in medicine, but other work was no less important to Wren.

The conceptual background to Wren's injection experiments lies in William Harvey's theory of the blood's circulation, and his most direct link with Harvey was Charles Scarburgh. Scarburgh had known and worked with Harvey in Oxford during the 1640s. The immediate stimulus, however, may have been the injection of poisons in nature. Dean Wren, in an extended note to Browne's Pseudodoxia epidemica, discussed the poisonous bite of the scorpion. The note shows how reflecting on this natural injection might lead to the idea of an artificial one. Its last paragraph reads: