Mary Karr, Lit: a memoir (New York: HarperCollins Publishers, 2009), 255. Shouldn't that be the road from Lourdes? This reminds me of a comment I once read in Books and culture to the effect that there are some diseases that we have never seen God heal.
I don't know about Zola, but here is Anatole France, in his essay on "Miracle" (The works of Anatole France in an English translation, ed. Frederic Chapman and J. Lewis May, vol. 12, 2nd ed. (London: John Lane, The Bodley Head; New York: John Lane Company, 1920), 176-177):
Happening to be at Lourdes, in August, I paid a visit to the grotto where innumerable crutches were hung up in token of a cure. My companion pointed to these trophies of the sick-room and hospital ward, and whispered in my ear: ‘One wooden leg would be more to the point.’ It was the word of a man of sense; but speaking philosophically, the wooden leg would be no whit more convincing than a crutch. If an observer of a genuinely scientific spirit were called upon to verify that a man’s leg, after amputation, had suddenly grown again as before, whether in a miraculous pool or anywhere else, he would not cry: ‘Lo! a miracle.’ He would say this: ‘An observation, so far unique, points us to a presumption that under conditions still undetermined, the tissues of a human leg have the property of reorganizing themselves like a crab’s or lobster’s claws and a lizard’s tail, but much more rapidly. Here we have a fact of nature in apparent contradiction with several other facts of the like sort. The contradiction arises from our ignorance, and clearly shows that the science of animal physiology must be reconstituted, or to speak more accurately, that it has never been properly constituted.’ . . . the man of science above surprise. . . . Such miraculous cures as the doctors have been able to verity to their satisfaction are all quite in accordance with physiology.
(That's actually quite consonant with a responsible Christian theology of both miracle and nature, by the way.)