AWAKENINGS By Oliver Sacks Summit. 339 pp. $18.95; paperback, $8.95 IVAN By Ivan Vaughan Farrar Straus Giroux. 201 pp. $16.95

When Ludwig Wittgenstein had completed the defense of his doctoral thesis, one of his examiners was so impressed that he concluded: "It is my personal opinion that Mr. Wittgenstein's thesis is a work of genius; be that as it may, it is certainly well up to the standard required for the Cambridge degree of Doctor of Philosophy." It is my personal opinion that "Awakenings," written by Oliver Sacks in 1973, is a work of genius; be that as it may, it is certainly well up to the standards required for republication. Amplified and brought up to date, "Awakenings" is Sacks' account of the dramatic -- and wrenching -- reversion to normal behavior of 20 patients suffering from far-advanced Parkinson's disease to whom he gave the "miracle drug" L-dopa. But "Awakenings" is not only a collection of astonishing case histories -- it is also a memoir, a moral essay and a romance.

Readers of Sacks' bestselling "The Man Who Mistook His Wife for a Hat" will find this earlier book equally engaging. Both succeed in expressing the joy he derives from "the fusion of scientific and 'romantic' penetrations, finding my mind and my heart equally exercised and involved, and knowing that anything different would be a dereliction of both." In "Awakenings" we experience what happens when the spell of longstanding disease is broken by the magic of powerful drugs. These patients with Parkinson's disease due to the sleeping sickness of 1916-1927 -- silent Magda B., trembling Rose R., twisted Robert O. -- awake in 1969 as if touched by a sorcerer's wand. But the drug turns out to be a mixed blessing: As described by Sacks, "awakening" is only the first act of a romantic melodrama. For some patients, time has stood still, while others "retained the power to remember, to compare, to dissect, and to testify."

In the second act, which Sacks calls "tribulations," the patients' moods, gaits and utterances rise and fall, swoop and flutter as the action veers between the turgor of too much, and the stupor of too little medication. These travails are "expressed in dramatic histrionic terms; the person shows forth in all his reactions, in a continual disclosure or epiphany of himself; he is always enacting himself in the theatre of his self."

Not only must the patient accommodate himself to the jagged performance of his new persona, but his physician also has to reach another level of knowing. Sacks describes that process on the part of the physician, of crawling beneath the skin of the hurt other, in the most masterful fashion.

The art of Sacks is based on his unsentimental refusal to use illness as metaphor and to regard it instead as an unfortunate, random act of nature that none can escape and some can transcend. If, as Joyce has remarked, sentimentality is unearned emotion, "Awakenings" earns its cumulative emotional impact not by giving us 20 case histories, but 20 stories, separate narratives of "physiology as it is embedded in people, and people as they are embedded and living in history."

"Awakenings" not only draws strength by virtue of narrative drive, but also rests on the pillars of clinical science. But it is in the epilogue that Sacks reaches his apogee in what is the finest meditation on the art of medicine since Sir Thomas Browne: "It is the function of medication, or surgery, or appropriate physiological procedures, to rectify the mechanisms which are so deranged in these patients. It is the function of scientific medicine to rectify the 'It.' It is the function of art, of living contact, of existential medicine, to call upon the latent will, the agent, the 'I,' to call out its commanding and coordinating powers, so that it may regain its hegemony and rule once again -- for the final rule, the ruler, is not a measuring rod or clock, but the rule and measure of a personal 'I.' These two forms of medicine must be joined, must co-inhere, as body and soul."

The internal and external dramas of the Parkinsonian agony are also described by Ivan Vaughan, an instructor at a teachers college in Cambridge, England. Victim of the disease and a schoolmate of the Beatles in Liverpool, Vaughan came to the attention of Jonathan Miller, who filmed a highly regarded television program about Vaughan's coping. This book is a brisk autobiography from which the author emerges as a man of pluck and honor, and whose wife deserves even greater praise. Written in artless style, it is nevertheless an affecting account of an "unsought crucifixion" -- Oliver Sacks' phrase -- the lessons of which can make sense only to the truly religious. The reviewer, a professor of medicine at New York University Medical Center, is the author of two books of essays, "The Woods Hole Cantata" and "They All Laughed at Christopher Columbus."