Booke 1:
An Introduction, or Compendious Way to Surgery.

For the surgeon to perform the aforesaid works, he must set before his eyes certain boundaries of working. Otherwise he will become a charlatan who acts boldly out of a blind temerity, and not by reason. These boundaries are drawn from things natural, not natural, and besides nature, and their adjuncts, as it is singularly delivered by the Ancients, being men of an excellent understanding. 

Natural things constitute and contain the nature of man’s body, which wholly depends on the mixture and temperament of the four humors, as it is shown by Hippocrates in his Booke de Natura Humana. Wherefore the consideration thereof belongs to that part of medicine which is named physiology; as the examination of things not natural to diet, because by the use of such things it endeavors to retain and keep healthy: but therapy, or the part which cures the diseases, and all the effects besides nature, challenges the contemplation of those things which are not agreeable to nature. The things which are called natural may be reduced to seven heads.