IN A LITTLE MORE than a decade, Lewis Thomas has established himself as America's foremost raconteur of science, a physician and a scholar able to probe and interpret the workings of human biology in a unique and gripping way. In two books of essays (The Lives of a Cell and The Medusa and the Snail) Thomas has shown himself to be a gentle essayist who captures the reader not so much by the power of his prose as by the erudition and poetry of his thought.

His achievement is the more remarkable because he became a writer virtually by accident. "I had not written anything for fun since medical school and a couple of years thereafter," he tells us in his memoir The Youngest Science: Notes of a Medicine-Watcher, "except for occasional light verse and once in a while a serious but not very clear or good poem. Good bad verse is what I was pretty good at." Yet 30 years after he left school, 30 years during which he became a prominent research scientist and medical administrator, a paper he authored on the improbable subject of inflammation led to an invitation by The New England Journal of Medicine to write a column for the Journal's pages. With some reluctance and, as it turned out, a great deal of success, Thomas set about producing a monthly piece under the heading "Notes of a Biology Watcher." Some time later, serendipitously, he received a letter from Joyce Carol Oates urging him to publish his growing collection of essays as a book . . . and the rest is literary history.

Thomas grew up with medicine. His father was a physician who graduated in 1905 and spent most of his career doing general practice and surgery in Flushing, New York. His father's experience, in Thomas' paradigm, was rooted in the pre-scientific era where compassion and placebo were the doctor's best tools. "There were so many people needing help, and so little that he could do for any of them. . . . Patients do get better, some of them anyway, from even the worst diseases. . . . If you are one of the lucky ones and have also had at hand a steady knowledgeable doctor, you become convinced that the doctor saved you. My father's early instructions to me, sitting in the front of his car on rounds, were that I should be careful not to believe this of myself if I became a doctor."

It was during his father's years of practice that the scientific method--the intellectual foundation of the soon-to-burgeon medical technology--found its way to medical research and education. But it was not until the late 1930s, when Dr. Thomas himself was a student at Harvard Medical School, that the science actually became a clinical reality with the "astonishing" cures produced by sulfanilamide, the first antibiotic. Drilled as students of that epoch were in the non-interventionary arts of diagnosis and prognosis, they watched the arrival of curative, scientific medicine with excitement and a touch of unease. "Medicine," Thomas observes, "was off and running."

The Youngest Science chronicles Thomas' rise as a partisan of the new scientific medicine, first as an intern in Boston, then as a research physician, department chairman, medical school dean and, for the last 10 years, chancellor of the Memorial Sloan-Kettering Cancer Center in New York City. Among the achievements that meant most to him was his establishment of a program at New York University in which a student could pursue MD and PhD degrees simultaneously, graduating as a physician-scientist, an officer in medicine's newly scientific army. Throughout, he writes about biology and humanity with modesty, lucidity, and a scholarly optimism that warms the heart of the reader chilled by frequent accounts of PCBs, Agent Orange and Swine Flu failures.

Though the tone of this memoir is characteristically quiet, there is nothing faint-hearted about its pronouncements. Cancer, Thomas states carefully but definitively, is caused by "a single determining mechanism" rather than a variety of different causes. This mechanism will be discovered and fixed so that he cleanly predicts "the end of cancer" by the end of this century. His observations are subjective as well. After describing his own experience with illness, he concludes, "I know a lot more than I used to know about hospitals, medicine, nurses, and doctors, and I am more than ever a believer in the usefulness of technology, the higher the better."

And yet, despite his faith in the system of which he is an architect and a symbol, he sounds one, faint note of question--a query that deserves careful attention. The modern medical center, driven by the popular desire for more sophisticated biomedicine, staffed, indeed, by MD-PhDs, and fueled by grants from the National Institutes of Health, has tended to dwarf the other faculties of most universities. More specifically the role of the medical school itself has been bent to the intriguing and consuming pursuit of research such that it has become "the accepted idea that every faculty member of every medical school in the country must be a working scientist with a grant from the NIH and a laboratory at his disposal."

Thomas does not lament this drift although it seems to trouble him just a bit. It is, indeed, a critical question for the future of medical training and practice in this country. Could medical education--scientific medical education--not be built on a premise other than that of research? Could good doctors, like Thomas' father, not be fostered and inspired in a setting other than one designed to discover the innermost secrets of the cell? Surely it would be less costly than our current model and, perhaps it might produce physicians more atuned to the rigors, the mundanities and the beauties of everyday clinical practice.

These are questions for the coming generation as medicine, the youngest science, continues to mature. For his part, Lewis Thomas has seen the modest medicine of his father transformed into the inventive, skillful, practical science of today. He has watched that process, he has partaken of it and now he has written vividly about it. More he could not have done.