By Lou Myers

Grove Weidenfeld. 193 pp. $17.95END NOTES

Unlike the other four boroughs of New York City, the Bronx is not part of an island but part of the Eastern Seaboard mainland. Perhaps it's a stretch, but one wonders if that is why Bronx memoirs seem more anchored to mainstream reality than counterparts set in Brooklyn, where nostalgia often rules, or Manhattan, where echoes of Europe are sometimes in the forefront.

Lou Myers's autobiographical novel, "When Life Falls It Falls Upside Down," is set in the same Depression-era streets as E.L. Doctorow's "World's Fair" and Kate Simon's "Bronx Primitive." And although it has moments of fantasy, for the most part it is rooted in the same kind of clear-eyed observation, punctuated with a thousand tiny details, that gave weight to those two distinguished works.

Myers, a cartoonist whose work has appeared in the New Yorker, begins his story in a West Bronx tenement in the 1920s. His alter ego, Leon, tells the story of his immigrant parents, especially his mother ("Drezzle" is her nickname from the Old Country), who keeps the orphanage at bay and raises her kids on her own after her mostly unemployed husband drowns one summer while swimming in the Jerome Park reservoir.

The scenes of daily life, harsh yet warmed by an unquenchable community spirit, are told in artless chapters that at first appear to be written down with no transitions. A story about picking a fight with a kid walking on top of a billboard, to use one example, follows one about riding the subway to visit relatives in Brooklyn.

Myers lets the reader hear the crackle as tenement dwellers step on gigantic cockroaches, feel the blows as young boys fight in the schoolyard, sense the suffering closeness of families forced to sleep on living-room sofas while boarders take over a bedroom. Gradually, the novel takes on the rhythm of a folk song, with a bingo game as the chorus. It seems to go on no matter who has just died. During the games, participants recite what amounts to an oral history of the Jewish immigrant existence.

In one sequence, for instance, the bingo players are reminiscing about an ambitious candy store owner who put his whole family to work, with unfortunate results: "Ma called '0-55' with a fresh card. 'Listen,' she said, 'Wally and Seymour began eating up all the jelly beans and the Tar Babies without bothering to reorder. Then they ate the Baby Ruths. They would sleep late and lose the morning newspaper sales ...'

" 'Sometimes,' Mrs. Wilkins continued, 'all five of them overlapped with more of them than customers. The bell on the door would tinkle, and if someone came in it was like the bell at ringside, all five jumping around for one egg cream. G-60.' "

Leon's memory delivers a mosaic of the Depression -- sex on rooftops (no one had private rooms, let alone cars or empty apartments); date night at the Loew's Paradise, a movie palace in the grand tradition; the ritual spouting of political slogans from Stalinists and Trotskyites; communist street demonstrations; entertaining park-bench audiences with costumes from the local theater group; demeaning jobs in the rag trade. The author does not judge his people or their actions. Like layers of paint, scenes pile up thickly on his canvas and grow into a three-dimensional portrait.

These chapters alternate with Leon's straightforward diary entries chronicling Drezzle's later descent into senility and delusion. There is a gentle humor in Leon's descriptions. Just as his recollections of growing up suggest an acceptance of the immigrant pilgrimage toward the middle class, rather than the more typical rebellion against it, so his jottings about the elderly are filled with understated compassion. How many sons have there been in fiction who visit their institutionalized parents with such faithfulness and attentiveness?

At the old age home, during what is apparently the 1960s, Drezzle becomes a member of the Women's Committee to Save Lives, a collection of residents dedicated to reviving suicidal patients. "Better ten times sick than once dead" is her motto. As the months wear on, however, she begins to believe the home's caretakers are demanding payment in foreign currency, letting outsiders rob the rooms of everything including the fixtures and are about to deport her.

One day, Leon finds Drezzle wearing her roommate's false teeth. She insists that a branch of a funeral home has been set up in the home; they accept American Express. Yet although one after another of her colleagues dies, Drezzle, now 90, sinks slowly and, somehow, not terribly painfully. She may mix up her younger son's first wife with the second, but with or without her wits, Drezzle is never mean or clutching. She is as benign a Jewish mother as fiction has produced in some time.

The reviewer, a New York-based writer, is a native of Brooklyn.