— Thomas Edison American inventor and businessman 1847 - 1931
This has been reprinted many times with slight variations on the wording; it is part of a much larger quote directly from Edison published in 1903:
:Nineteen hundred and three will bring great advances in surgery, in the study of bacteria, in the knowledge of the cause and prevention of disease. Medicine is played out. Every new discovery of bacteria shows us all the more convincingly that we have been wrong and that the million tons of stuff we have taken was all useless.
The doctor of the future will give no medicine, but will instruct his patient in the care of the human frame, in diet and in the cause and prevention of disease.
They may even discover the germ of old age. I don't predict it, but it might be by the sacrifice of animal life human life could be prolonged.
Surgery, diet, antiseptics — these three are the vital things of the future in preserving the health of humanity. There were never so many able, active minds at work on the problems of diseases as now, and all their discoveries are tending to the simple truth — that you can't improve on nature.
:* As quoted in "Wizard Edison" in The Newark Advocate (2 January 1903), p. 1 according to research by Barbara and David P. Mikkelson at snopes.com http://www.snopes.com/quotes/edison.asp.