The Vaccine Vesicles

Plate from 'A Treatise on the Cow-pox: Containing the History of Vaccine Inoculation, and an Account of the Various Publications which Have Appeared on that Subject, in Great Britain, and Other Parts of the World' (1803) by John Ring.
Also known as vaccinia, cowpox a is a disease caused by a virus related to variola (the virus responsible for smallpox). It is most common in animals and can be transmitted to humans by cows.
The plate illustrates the 'course of the vaccine pustule'.