I am annoyed at a failure of my education that I only last week came across another famous-in-his-day GP who paid attention. Will Pickles was a doctor in Aysgarth from 1912 to 1965. Where? Aysgarth! An obviously Norse name, [meaning any of: the garden of the gods, water of rocks or the enclosure of oaks] it is a village about midway up the valley of Wensleydale in Yorkshire. The mappe with antient fonts delimits the extent of Dr Pickles' practice:
source]. Even with his capacious memory this was only really possible because, with the help of his diligent wife, he captured the names, dates and locations of everyone who fell sick.
dysentry, however, appears to have started at Askrigg and then moved East to Aysgarth. If you pay attention you can calculated the incubation period for each disease. The spikes of new cases of measles in West Witton occur every 10 days while the blips of influenza in West Burton are separated by about 2 days. With similar data analysis, Pickles was able to reveal the incubation period for catarrhal jaundice [aka infectious hepatitis] was 25-35 days; nobody knew that before.
The data from measles in W.Witton is particularly instructive w.r.t. herd immunity. You get one case at the beginning of January 1932; 6 more cases 10 days later; 14 cases 10 days after that; and 7 cases 10 days afterwards. At that point everyone in the village who is infectable has been infected and the measles virus has no place to hide / reproduce. End of measles epidemic. With vaccination, you'd drastically reduce the number of susceptible people and the epidemic would peter out earlier . . . before Betsy Snitterthwaite comes visiting from Carperby and carries the virus to fresh fields up the valley.