Prior to the birth of modern medical theory, the pervading thought for illness was that disease was caused by an imbalance of body fluids. To right this, common medical practices included purging, starving, blistering or blood-letting to place things back in order.
Maybe you think we don’t use any of these practices anymore. Think again.
Let’s consider blistering a patient.
In historical medicine, blistering used a caustic substance on a portion of the patient’s skin to induce a burn or blister. The goal was to create infection as physicians of the day thought that the subsequent puss draining from the wound would be beneficial for the patient.
You can read more about that here: http://www.childrensmemorial.org/depts/dermatology/mollus.aspx
Does it surprise you that a blistering agent is still used as a medical treatment?