"To the memories of Digit, Uncle Bert, Macho, and Kweli."

Extraordinary sadness is reflected in Dian Fossey's dedication of her excellent book to four mountain gorillas, once vital members of a threatened species of apes that survives today only on a narrow strip of land stretching across the misty slopes of six extinct volcanos in central Africa.

It is a personal sadness for Fossey, a remarkable scientist for whom the four became almost like friends; and it is a sadness for the world at large, because--despite all of Fossey's protective efforts--three of the four were slaughtered by poachers, and the orphaned Kweli, a 3-year-old male, died of a broken heart a few months later. Her account of the killings--she calls them "murder"--is a warning of the potential fate faced by the few remaining mountain gorillas, by her count no more than 240, as humans encroach on their rain forest preserve.

For 13 years Fossey lived and worked in the remote mountain habitat of the mountain gorillas, a rugged region that crosses the borders of Zaire, Uganda and Rwanda. The bulk of Fossey's studies concern four main groups of gorillas, totaling 51 members, who lived in a 9.5-square-mile area around her camp, the Karisoke Research Centre in Rwanda. She found that, like human families, they exhibit a full range of characteristics: They are playful, helpful and caring to one another as well as sometimes quarrelsome and bullying. Some parent gorillas are attentive and loving, others curiously neglectful.

As fascinating as are the revelations about the gorillas, Fossey's book is even more a deftly told adventure story in which she emerges as a reluctant but courageous hero. Unable simply to watch and record--challenge enough in this lonely wild--Fossey organized the only effective antipoaching force and even joined a police sweep to round up notorious animal trappers.

Her spirit is evident from the outset. When her sponsor, the famed Dr. Louis S.B. Leakey, informed her it would be mandatory to have her appendix removed before she entered gorilla country, she dutifully underwent the operation. Returning from the hospital, she received a letter from him saying the demand was only "my way of testing applicants' determination."

Initially, she established her research station in Zaire, but it was hardly under way when a coup erupted and she became a captive pawn. By using her wits, she eluded her drunken guards and fled across the border in her Land Rover. A short time later, she set up her new camp in Rwanda, which from 1967 to 1980 became a mecca for students and scientists from many countries.

Fossey's time in the field, she says in something of an understatement, was "exciting" because of "the near daily encounters with elephant, buffalo, giant forest hog and, of course, gorilla." Once, crawling through dense foliage, she grabbed what she thought was a sapling trunk. Instead, it was the leg of a startled African buffalo, which dragged her through a bed of nettles until she could let go.

Some 21 workers came to Karisoke to help her research work over the years, and for the majority of them life there proved too difficult. "It never dawned on me," she writes, "that exhausting climbs along ribbons of muddy trail, bedding down in damp sleeping bags, awakening to don wet jeans and soggy boots, and filling up on stale crackers would not be everyone's idea of heaven."

A sense of humor is a strong ally in adversity, and Fossey was well supported in this regard. In the early days, chancing on a gorilla group, she attempted to climb a tree to get a better view. The tree was slippery and "no amount of puffing, pulling, gripping and clawing succeeded in getting me more than a few feet above ground." She was convinced her noisy efforts had frightened the shy bunch away. But no, "I was amazed to look around and find that the entire group had returned and were sitting like front-row spectators at a sideshow. All that was needed to make the image complete were a few gorilla-sized bags of popcorn and some cotton candy." Gorillas, she learned from the incident, are insatiably curious.

Two young orphaned gorillas gave her some of her "most joyful" hours, but they also brought pain. Park officials, seeking a gorilla for a European zoo, had captured first one and then the other, slaying the parents and several others in the gorilla families to do so.

In the shock of the capture, and their subsequent treatment, the two survivors began deteriorating rapidly. That's when Fossey's help was sought. At one point, she even carried the first of the orphans, Coco, to bed with her "for what I assumed would be her last night alive. Warmth and security was all that I could provide." The treatment proved a success. "The next morning, instead of finding a corpse in my arms, I found Coco still alive and both of us lying in a bed soaked with diarrhetic dung."

In her care, Coco and Pucker slowly regained their vitality, becoming playful and affectionate delights. But the zoo continued to want a gorilla, and park officials insisted that pair be delivered. Fossey ultimately acquiesced "to avoid further slaughter." It was, she writes, "one of the biggest compromises I had to make . . . There is no way to describe the pain of their loss, even now, more than a decade later." Within a few years, Coco and Pucker died in their new home.

In the end, Fossey's book is an appeal for increased efforts to preserve the home of the last mountain gorillas. But, "the question remains," she warns, "is it already too late?"