Eighteenth century medical practices were primitive and were based on an only rudimentary understanding of the human body. Medicine had changed very little from the days of its pioneering theorists, the ancient Greeks and Romans - Aristotle, Hippocrates, and Galen. Galen's theory of the four vital "humours" - blood, phlegm, black bile, and yellow bile - was the basis for almost all medical practice. Most doctors did not study their patients' symptoms. Instead, they assumed that if a person was ill, one of their humours was out of balance, and treated the patient accordingly.
Bleeding was the most common course of treatment. The theory went that if you removed the patient's blood, the body would be relieved of that overproduced humour and could then function more freely with what was left. Doctors applied leeches to suck the blood away, or they would engage in "bloodletting" - slicing small cuts in the flesh to allow blood to drain off into bowls. This treatment was recommended for a variety of diseases, including inflammatory fevers, coughs, headaches, rheumatism, abscesses and some forms of heart disease. Bloodletting was also routinely performed as a preventive measure. The diary of an 18th century medical practitioner was typically filled with notes such as "The wight with the Shivered Skull now awake, but very confused in his wits; did bleed him seven ounces, and throw up a Clyster these to divert his blood from his head."(12)
To encourage blood flow during a bloodletting procedure, the barber-surgeon commonly gave his patient a pole to hold and squeeze. He also used a strip of cloth as a tourniquet, later applied as a bandage when the operation was finished. Originally, when it was not being used, the pole with the bandage wound around it was hung at the barber-surgeon's door as a sign. Later, for convenience, instead of using the actual pole, an imitation was painted and hung outside of the shop. This was the beginning of the modern barber pole.
Read more about Galen's theory of the four humours