The young Sigmund Freud gave himself cocaine as "a therapeutic experiment."

He ultimately discovered the dangers of this insidious drug. Yet he established its value as a muscle-numbing anesthetic, and his experiments of the 1880s led to some of the first successful operations on the eye, an organ whose constant movement had until then made complicated surgery all but impossible.

The story of Freud and the many other scientists who have made themselves their own guinea pigs -- and sometimes thereby suffered or died -- is told for the first time in a remarkable new book by Dr. Lawrence Altman, a physician and a reporter for The New York Times. "Who Goes First? The Story of Self-Experimentation in Medicine" (Random House, $22.50) is a signal work of medical history.

The book also offers some advice to patients considering taking part in medical experiments themselves. Ask the experimenter: "Have you done this first?"

The answer cannot and should not always be yes. But sometimes it should be, and if it is not the patient might want to say no.

In 1949 Dr. Hilary Koprowski -- a Polish refugee who would become one of the world's leading virologists -- injected himself with an experimental tick fever vaccine, and found that it caused undesirable side effects, including fever and headaches. It was one of several times over the years when he would try experimental vaccines, including some containing potentially fatal rabies virus, on himself.

"If those of us who developed the vaccine were going to recommend that other humans take it," he explained, "it was incumbent on us to show our own confidence in it by injecting it into ourselves first. It was only fair . . . to say that we had put ourselves on the line first and that we were not afraid."

Experimentation -- systemized trial and error -- is essential to medical progress. As Altman says, "Everything that is now standard in medical practice was once experimental."

Medical scientists of course study animals. But animals' reactions are not just the same as our own, and sooner or later men and women must become subjects.

At this point there is inevitable risk. "Experiments with humans are voyages into the unknown," Altman writes. "The potential for death, injury or illness can be reduced, but it cannot be eliminated."

"It is only when I can tell that I can surely vaccinate dogs who have been bitten that I would dare to experiment on man," said Louis Pasteur of his search for a rabies vaccine. "And yet my hand should shake because what is possible on the dog may not be so on man."

It is this inevitable risk, Altman tells us, that "leads to the fundamental question . . . Who goes first?" ::

A young German doctor, Werner Forssmann, in 1929 asked his superior for permission to insert a long tube into a vein in his own arm and shove it all the way into his heart. His superior said no -- the risk was too great.

Forssmann did it anyway, pointed the way to cardiac catheterization -- now a standard diagnostic procedure -- and ultimately won a Nobel prize. ::

Not all scientists agree they should be first. Last year a French scientist, Dr. Daniel Zagury, injected himself with an experimental AIDS vaccine containing a protein from the AIDS virus' outer layer. He did this in conjunction with a trial of the substance in Zaire. He showed that the substance at least stimulated some anti-AIDS antibodies.

He was criticized by some fellow scientists. "I think they felt he was grandstanding," says one American researcher.

Some also may have thought, "If Zagury does this -- and publicizes it, as he did -- must I do it too?"

Self-experimentation by scientists is not always wise or appropriate. "The self-experimenter may lose perspective" and be a highly biased observer or take needless risks, Altman points out. "Mentally unbalanced individuals may be tempted to do crazy things," then repeat them on others.

Self-experimentation is often impossible -- in surgery, for example, or where the experimenter is too old or unhealthy. Still, Altman argues, "physician-researchers have learned that if they really want to learn what their patients are going to experience, there is no substitute for taking a drug {or other treatment} themselves."

Self-experiments also "clarify thinking," he says, improve experiments and may help avoid unnecessary and even hazardous effects. One British scientist also told him, "It's much easier to get the volunteer's cooperation . . . if you say that you have done the same experiment on yourself and are none the worse for it."

Many researchers will welcome the new and bright light Altman casts on this little discussed subject.

Others may less happily see it as one best left unpublicized, lest they indeed be asked, "Have you gone first?"

Altman would not extend them much sympathy. "Short of legislation," he argues (and he does not seek legislation), public awareness could "force more researchers to apply the Golden Rule."

Next Week: Should you take part in a medical experiment?