THE brightest and most optimistic of my presentiments about the future of human health always seems to arouse a curious mixture of resentment and dismay among some very intelligent listeners. It is as though I'd said something bad about the future. Actually, all I claim, partly on faith and partly from spotty but unmistakable bits of evidence out of the past century of biomedical science, is that mankind will someday be able to think his way around the finite list of major diseases that now close off life prematurely or cause prolonged incapacitation and pain. In short, we will someday . . .