In the first edition (1899) of "The Merck Manual," tobacco was listed as a cure for nymphomania: "tobacco, so as to cause nausea. Effectual, but depressing . . ."

And as recently as 1975, Merck wouldn't sell its manual to anybody but doctors and nurses and a few other health specialists.

"We'd just refuse orders from members of the general public," recalls Dr. Robert Berkow, editor in chief of the 2,696-page edition of what is proudly hailed as "the best-selling medical textbook in the history of the world," with entries ranging from "Abdomen" to "Zygomycosis."

However, on reflection, the powers-that-be at Merck decided that, after all, anybody was entitled to buy the fat (two inches of onionskin) little (8 by 5 1/2 inches) concise description of virtually every disease, symptom and treatment known to modern medicine.

"Of course," warns editor Berkow, "we don't edit it for the public, and with the highly condensed style and the complexity of medical jargon, at the least they would waste their money {$21.50}, and at the worst they might get upset and confused by what they read."

Still, he concedes, a lot of people do read it, and sometimes it can be useful. For example, he got a letter recently from a nurse who swore that the book helped her save her daughter's life. "Nevertheless," he said, "we don't promote it to the general public."

Since 1950, the manual has had Spanish and German language editions. A few years ago, an Italian edition was added and became an instant best-seller in Italy. The current edition, the 15th, out since last fall, is being translated into French, Portuguese and probably Chinese. The previous edition sold about 800,000 copies. This latest one will probably top a million. ("Better," gloats the pharmaceutical house's publicity material, "than most novels.")

Berkow, who has headed the editorial operation for nearly 15 years, says it is "the oldest continuously published medical textbook in America and the second-oldest English-language medical text in the world," the first being a "small pathology book from England."

In fact, the 15 editions of the manual are, in themselves, an instant history of modern medicine.

The first edition in 1899 listed 10 aphrodisiacs (including strychnine; something called "nux vomica" that contained strychnine and "caused blistering of the skin"; cantharides, also known as Spanish fly; and gold) as well as 96 (ineffective) treatments for gonorrhea. "Today," notes Berkow drily, "we'd tend to recommend psychotherapy" instead of aphrodisiacs, and "gonorrhea is an example of the point that the more we know about a disorder, the fewer treatments we tend to have for it."

The second edition (1901) listed aspirin for the first time. AIDS, acquired immune deficiency syndrome, is mentioned for the first time in the new edition.

Acupuncture was mentioned in early editions but, said Berkow, was dropped in the 1920s.

The 11th edition (1966) talks about the effectiveness of "psychotherapy (hexing)" in the treatment of warts, especially in suggestible children, although it concedes that the tendency of warts to disappear spontaneously may have something to do with the effectiveness of the so-called hexes.

The last couple of editions don't talk about hexes but do mention the new drug interferon in connection with wart therapy and include a relatively long section on the placebo effect, including its origins:

"The term harks back to the 116th Psalm in the Hebrew Bible. Through a number of translating errors, the Vulgate Latin version came to contain the word 'placebo' (I shall please) . . . In 1785, the word placebo appeared in a medical dictionary for the first time as 'a commonplace method or medicine.' Two editions later, the placebo had become a 'make-believe medicine,' allegedly inert and harmless."

The current manual concludes, "We now know that administration of placebos may have profound effects, both good and bad." It even cites two "placebo addicts," one of whom "showed many of the characteristics of a true drug addict: a tendency to increase the dose, inability to stop the 'medicine' without psychiatric help, a compulsive desire to take the tablets and an abstinence syndrome when deprived of the tablets."

According to Berkow, changes since the 1966 edition have reflected changes in medicine that "are almost like a different world."

For example, he said:

Immunology: "It now pervades almost every area of medicine and hardly existed as a specialty 20 years ago. Oh, there was the old-fashioned allergy business -- hay fever and such -- but none of the real immunological stuff that we have today."

Neonatology: "Intensive care of the newborns in trouble barely existed at that point."

Cardiovascular disease: "In the last decade, we had to literally double the cardiovascular section because of the advancements. Moreover, he noted, "there are new disorders -- really new, like AIDS -- and some that may not be new but are more recently discovered and clarified, like Lyme disease."

Lyme disease is a good example of how the manual moves ahead, edition by edition. The disorder, which scientists now know to be carried by ticks, was identified first in the mid-1970s around Lyme, Conn. By the 14th (1982) edition, the editors were prepared to say, "Etiology {cause} is unknown, but strong circumstantial evidence favors transmission of a causative agent by the minute tick Ixodes dammini."

The current edition states, "The illness is caused by a newly discovered spirochete, Borrelia burgdorferi, transmitted by the minute tick Ixodes dammini and related ticks."

"On the other hand," Berkow notes, "if we go back to the 1899 edition, some of medicines prescribed then are still in use." These include nitroglycerine, used in cardiac conditions, and the pain-relieving codeine. ::

The Merck family of Darmstadt, Germany, opened an apothecary shop in 1668. From this small beginning would grow the huge Merck, Sharp & Dohme pharmaceutical company. The manual is published by the Merck Co. Foundation, the firm's educational arm.

Berkow came to "The Merck Manual" in mid-life and mid-career nearly 15 years ago. He was 45, a practicing internist and teacher at the University of Rochester Medical Center in Rochester, N.Y. He commuted between the Merck offices in Pennsylvania and Rochester for a year, then decided to cast his lot with the editing. Some 275 medical experts submit various portions of the manual, which then becomes a major editing and condensation job, Berkow says. "We like it to read as though it were written by one person."

As far as he knows, there is only one major gaffe in the current edition -- erroneous treatment advice for the rare inherited liver and kidney condition called Wilson's disease.

A couple of typographical errors caught in galleys still give him nightmares.

One of them "had a statement advising physicians treating adolescents to behave in a friendly manner but not to try to be a buddy. 'Friendly' came out 'fiendly.' "

Another entry said that women with lupus need not avoid pregnancy but are at risk of "post-mortem flares" of their condition. They meant postpartum.

Although Berkow and his team are reluctant to admit it, "The Merck Manual" has become a mainstay for many new parents, hypochondriacs and other members of a public so health-conscious that they have long since graduated from the "Physician's Desk Reference" (PDR) to the more graphic, albeit lofty, descriptions of fevers, syndromes, tumors, warts and disorders described in Merck.

Where else can you learn the difference between Tsutsagamushi disease and Dumdum fever?