As to diseases, make a habit of two things — to help, or at least, to do no harm.

Epidemics, Book I, Ch. 2, Full text online at Wikisource | Paraphrased variants | Wherever a doctor cannot do good, he must be kept from doing harm. | Viking Book of Aphorisms : A Personal Selection (1988) by W. H. Auden and Louis Kronenberger, p. 213.

The physician must be able to tell the antecedents, know the present, and foretell the future — must mediate these things, and have two special objects in view with regard to disease, namely, to do good or to do no harm.