All parts of the body which have a function, if used in moderation and exercised in labors in which each is accustomed, become thereby healthy, well developed and age more slowly, but if unused they become liable to disease, defective in growth and age quickly.

A wise man ought to realize that health is his most valuable possession.

Primum non nocerum. (First do no harm)

I also maintain that clear knowledge of natural science must be acquired, in the first instance, through mastery of medicine alone.

Opposites are cures for opposites.

In acute diseases the physician must conduct his inquiries in the following way. First he must examine the face of the patient, and see whether it is like the faces of healthy people, and especially whether it is like its usual self. Such likeness will be the best sign, and the greatest unlikeness will be the most dangerous sign. The latter will be as follows. Nose sharp, eyes hollow, temples sunken, ears cold and contracted with their lobes turned outwards, the skin about the face hard and tense and parched, the colour of the face as a whole being yellow or black.

The physician must have at his command a certain ready wit, as dourness is repulsive both to the healthy and the sick.