Epidemics of the plague and other killer diseases, such as smallpox, the Great Pox (syphilis) and sweating sickness, could not be easily explained by the Theory of the FourHumours
In 1628, a new theory was published in Britain, which suggested that bloodcirculated around the body instead of being made in the liver, as taught by Galen
In 1676, the medical textbook Observationes Medicae was published. This to theorised that illness was caused by external factors rather than the four humours.
However, there was no point studying correct drawings of the internal organs when it was impossible to diagnose or treat internal problems on a living patient
By the end of the 17th century doctors and scientists had lots of new ideas about the causes of illness and disease-it just wasn't applied to everyday medical practice