Two hundred years ago, the English physician Edward Jenner published a book of revolutionary significance. An Inquiry into the Causes and Effects of the Variolae Vaccinae recorded Jenner's success in 1796 of producing immunity to the dreaded disease of smallpox. After learning that people exposed to cows frequently acquired immunity to smallpox after contracting a milder disease called cowpox, Jenner decided to experiment. He inoculated a young boy with cowpox pathogens obtained from an infected dairy maid. After the child recovered from the slight fever caused by cowpox, Jenner inoculated him a second time with smallpox. In Jenner's test, this second inoculation failed to take effect. The boy was already immune.

Jenner's vaccination was applauded around the world, and has been celebrated ever since as one of the great events in man's "conquest" of disease. In his provocative history of medicine, The Greatest Benefit to Mankind, Roy Porter takes a more clinical view of Jenner's achievement, and of the triumphal claims of medical science it inspired. Can humanity actually "conquer" disease, or is the occasional victory over one of its myriad forms the best we can expect?

Porter's book is not a revisionist debunking of humankind's effort to eradicate disease. Porter is a judicious historian who teaches at the Wellcome Institute for the History of Medicine in England. He is an accomplished writer as well, marshaling the salient facts, key personalities, and demographic trends of man's medical past in luminous, compelling prose.

Although written for nonspecialists, Porter's book can be studied with advantage by serious scholars of medical history and biomedical researchers in general. For along with a balanced assessment of the impact of disease upon the course of civilization, the author provides unsettling insights into the human response to these maladies. Pathogens infiltrating the human body produce disease, but often it is the social infrastructure of humanity that turns these unseen intruders into epidemics.

Porter traces the evolution of human society, the growing menace of threatening diseases, and the rise of the medical profession as concurrent, interrelated developments. With a discerning eye, he shows how the agricultural revolution 5,000 years ago exposed human beings to forms of illness that their hunting, nomadic ancestors had evaded. Pathogens from domesticated animals, parasites absorbed during irrigation, work in marshy areas, and unbalanced diets low in protein and vitamins were the deadly price humans paid to reach "civilization."

History's early epidemics offered both protection and destruction. In many cases, survivors acquired a natural immunity, which they passed down to succeeding generations. But when these biologically toughened groups encountered unexposed tribes and civilizations, the results were fresh outbreaks of cataclysmic disease. Porter describes the waves of measles, influenza, smallpox and typhus, which marched with the Spanish conquistadors through Mexico and Peru in the 1500s, as "the worst health disaster there has ever been . . . the conquest of the New World by the Old World's diseases."

The pages of medical history also record intellectual interplay between civilizations. Porter writes movingly of the way Muslims, Christians, and Jews preserved and shared the treasures of Greek science during the Middle Ages. Indeed, they were held in thrall by the sheer brilliance of the Greco-Roman tradition to the detriment of their own creative powers. The iron grip of Galen, Aristotle, and other ancient sages on the Western world would not relax until the nineteenth century.

Porter covers the medical traditions of India and China in separate chapters that detail their contributions and motivating ideals. Nor does he condescend when treating the healing arts of so-called primitive peoples in remote areas of the world. His book, however, has a definite Europocentric focus, and he is convincing in explaining why: "What began as the medicine of Europe is becoming the medicine of humanity."

The decisive moment leading to the ascendancy of Western medicine occurred during the Renaissance of the sixteenth and seventeenth centuries. In mercantile cities in Italy and the low countries, an impatience with hallowed social custom seeped into scientific thought. The anatomical studies of Andreas Vesalius and Gabriele Falloppia were notable examples of the new "show me" science based on direct observation and methodical classification.

Yet these extraordinary gains in pure science had a very limited effect on medical practice. Epidemics continued to ravage Europe's crowded cities. Indeed, the antipathy of the medical profession toward midwives and folk healers added to the death toll. Doctors, with no idea of the germ theory, went straight from dissecting corpses to treating ailing children or delivering babies - quite often to an early grave.

Jenner's cowpox experiment marked the long-delayed moment when medical theory and health care effectively joined forces. As visionary researchers like Louis Pasteur and Robert Koch began to apply the scientific method and new technological tools to the study of disease, the life sciences in Europe and the United States developed a dynamic for innovation never before witnessed. "In the twenty-one golden years between 1879 and 1900," Porter writes, "the micro-organisms responsible for major diseases were being discovered at the phenomenal rate of one a year."

With the medicines and vaccines that followed from these discoveries, an educated person at the turn of the twentieth century could indeed expect the coming decades would continue the golden age. Instead, the rate of medical discovery has been matched by the escalation of diseases, both psychological and physiological, caused by the stress of modern life. And the medical profession itself has been implicated in some of the more dubious campaigns of social engineering, ranging from Nazi racial genocide to the use of human guinea pigs in cases such as the Tuskegee syphilis experiment in the United States.

Porter's ability to integrate this vast body of material within the framework of his narrative is extraordinary. He never loses sight of the character traits of his protagonists. Nor does he forget the sufferings of humanity are those of flesh and blood individuals. When he writes of the needless deaths of thousands of mothers during childbirth in Victorian England and America, his words convey a sense of outrage at the medical profession's callousness.

The real problem with the life sciences at the dawn of the new millennium is that they are victims of Western medicine's success. Inflated expectations of the efficacy of medical science are based on real triumphs. This in turn has led to the idea that medicine can be treated as a commodity, a product to be dispensed like a prescription dashed off by an overworked physician to mollify a needy patient.

Porter is scathing toward the concept of medical consumerism. Yet, despite the spread of new threats like AIDS and ebola or the return of others like malaria in a more virulent form, he is not without hope for the future, since "medicine's finest hour is the dawn of its dilemmas."

The Greatest Benefit to Mankind is that rarest of books, simultaneously a cautionary tale and a source of inspiration. It is a testament to what the human mind can achieve, if it is not weighed down by outmoded traditions or beguiled by the sound of trumpets.