CONSIDER the human brain. A two-pound lump of wizardry, the brain comprises trillions of brain cells connected to each other, cells that communicate through chemical secretions and electrical firings. Somewhere deep inside the grayish jelly is the right combination of secretions and firings that makes us who we are. The brain regulates our breathing, heartbeat, digestion without our even knowing it, and at the same time directs our thinking, our behavior, and the movements that are under our conscious control.

But most remarkable is the fact that the brain is capable not only of all these tasks, but of self-examination as well. The human brain is the only organ on earth that is aware of itself.

Now consider cutting into the brain. One wrong turn and you come perilously close to the brain stem, where basic life functions begin. One wrong gesture and you touch the thalamus, and the patient awakes in agony. One wrong cut and you sever the anterior inferior cerebellar artery (the AICA, or what brain surgeons call the aye-ka), and a few days later the patient will die. One mistake and you do irreparable damage to the very essence of the human personality--or leave the personality untouched while turning the body into a prison of paralysis.

Brain surgeons know, of course, how closely danger lurks. Using microscopes, tweezers, and tiny, tiny suction tubes, they bring their patients perilously close to death with each minute gesture. The drama of a brain operation, like the drama of a circus high-wire act, is gripping and immediate. It is also a bit macabre: a misstep means that someone will die, or change forever.

Jon Franklin and Alan Doelp, co-authors of Not Quite a Miracle, know how to make best use of our eerie fascination. They recount in painstaking detail the brain operations, and the lives and hopes, of four brave patients. Every time blood floods into the surgical field, every time a crucial nerve or blood vessel retracts into the folds of the brain, we are told about it. And we hold our breaths. Will the patient live? If he lives, will he ever be the same?

The awesome stakes of neurosurgery are what keep us reading this impressive book. As we read the play-by-plays of a half-dozen grueling operations, we receive along the way a mini-course in neuroanatomy, neurochemistry, and neuropsychiatry. We are impressed with the strides that have been made in the past decade in scientists' understanding of the brain, in their new knowledge, for example, of the link between chemicals and emotion. But at the same time, we marvel at the comparative crudeness of brain surgery itself.

The instruments of neurosurgery are surprisingly primitive: scissors, clippers, scrapers, wads of cotton, sprays of water. And, even in 1983, the most crucial tools are what they have always been: a surgeon's hands--and his patience.

"The OR (operating room) was cool, almost chilly," the authors write in the book's best scene, "but as Dr. Long worked so close to the basilar (the artery that supplies the brain stem), tiny beads of sweat appeared on his forehead. Millimeter by agonizing millimeter, he worked his way along the tumor capsule, snipping, probing, snipping, probing. Slowly, in the background, the brain stem appeared. It glistened in the lights. There was tumor stuck to it, too.

"Slowly, slowly, a blunt instrument swam into view and, ever so lightly, touched the brain stem.

" 'Watch him,' Dr. Long warned the anesthesiologist. 'My right-hand retractor's on the brain stem. Tell me if he changes at all.'

"The heart beat steadily, ka-GLUP, ka-GLUP, ka-GLUP.

" 'Is he changing at all?'

" 'No. He's stable.'

" 'I'm right on the basilar now.'

"Steady, seventy-five beats a minute.

"With the probe, Dr. Long stroked the tumor capsule where it clung to the basilar. The capsule remained stuck."

The rhythm of the operating room prose is precise, repetitive, urgent. The ultimate effect is to make one stand in awe of these surgeons' extraordinary calm. How can they bear to work in such tiny gestures? How can they bear to take so long to advance one centimeter? How can they bear to attend to the same details--the 10-minute scrub, the drilling into the skull, the endless scraping away and teasing off of the stuff that doesn't belong in the brain--time after time?

"Slowly. Time and patience.

"Not pulling, tugging, except not quite tugging, urging. By watching the television screen, the scrub nurse followed the operation, anticipating which tools Dr. Murray would call for.

"Suction. Cotton ball. Microscissors. Suction. Irrigation. Suction. Bayonet. The aye-ka is right there. Cotton ball. Beep, beep, beep, beep, beep, beep."

In addition to a full store of surgical and physiological facts, the book contains some good cocktail-party bits of information. Did you know, for example, that even though technicians can produce computerized brain scans in four-color, three-dimensional images, they still print a few black-and-white negatives on photographic film because brain surgeons feel more comfortable reading x-rays that way? Did you know that brain surgeons don't drink coffee on the morning of an operation, because it makes their hands shake? Did you know that brain surgeons often must stand up through their 9-or 12-hour operations without stopping for a bathroom break?

Not Quite a Miracle is not quite perfect. The authors get too cute at times: referring to one patient for an entire chapter as Case No. 191-00-18; having surgeons meditate on operations past, present, and future in ways I doubt ever got meditated; thrusting the reader into a neuroanatomy lecture at the University of Maryland medical school. The authors try to bring us into the thoughts of patients and surgeons, sometimes with awkward results; awkward, too, are their attempts at heightening the dramatic tension by ending one patient's story midway in the telling and shifting abruptly to another's.

And I frequently yearned for some drawings or photographs: What does a "sucker" really look like? Where is the anterior inferior cerebellar artery in relation to the cerebellum? What does it mean to operate on a pituitary tumor by "lifting" the patient's face away from her skull?

But I couldn't put the book down. The personal background supplied for our heroes might have been awkwardly handled, but it did indeed turn them into more than cardboard actors. By the end of the book, I really cared acout the patients--Josh, Joe, Richard, and Tony-- and I didn't want them to die. I read the blow-by-blows of their operations as though I were reading a novel, and when Joe suddenly moved on the operating table six hours into the surgery to extract his huge tumor, I jumped too.

Franklin and Doelp kept me constantly aware of the tremendous stakes in every operation. And that's what makes the book so powerful. The first rule of neurosurgery, as expressed eloquently by Dr. Michael Salcman, one of the four neurosurgeons profiled here, is as simple, and as gripping, as a brain operation itself: "Don't ever pull on anything. Not ever. You don't know what it's attached to. It might be attached to something that's attached to something that's attached to the soul."