‘Nothing is so dangerous to its surroundings as a syphilitic infant.” So wrote Alfred Fournier, a prominent French doctor whose exaggeration, back in the late 19th century, would be hard to blame. In southwestern France, a contaminated newborn had recently infected his unsuspecting wet nurse, and when she fell ill her neighbors, equally unwary, took her place in between nursing their own children. Before long, 40 people were mottled with telltale lesions.

Italians liked to call syphilis “The French Disease,” but it was hardly that provincial. During Fournier’s time, 10 percent of the urban men in Europe were infected, almost invariably through sexual contact, and Italy was experiencing, if anything, a renaissance of transmission. The widespread infection of Italian wet nurses, however, was more circuitous than the usual indiscretions, and also far more sad.

As a matter of appearances, Italian law forbade women from raising children born to them out of wedlock. Thousands of babies every year took their first breath already fatherless, and their mothers, usually the rural poor, had no legal choice but to abandon them to a foundling home for bastardini, or “little bastards.” Hospital-run foundling homes paid desperate peasants to take orphans back to the countryside and keep them fed; each would be the other’s meal ticket. Since venereal disease is, quite literally, the bedfellow of promiscuity, illicit offspring were often infected with syphilis — and soon enough, so were their wet nurses.

“Amalia’s Tale” (Houghton Mifflin, 256 pages, $24) purports to be the true story of an Italian wet nurse — an illiterate peasant named Amalia Bagnacavalli — who was disastrously infected by such an infant in 1890, but it is really the story of her lawyer, Augusto Barbieri, and of the decade-long legal crusade he fought on her behalf.

By suing the Bologna city hospital that hired Amalia, Barbieri savvily cast himself as a civil rights advocate in a country where, he argued, fat rich feet stamped carelessly on the starving rural poor. The suit caught national attention partly because it allegorized a pivotal transition: In fits and starts, the destitute masses of the Italian countryside were awakening to the inequities of their social stratum. Labor strikes, anarchist uprisings, and socialist fervor were themselves becoming contagious. For David I. Kertzer, the book’s prolific author, Amalia is a carrier of this polarized moment in history.

“Amalia’s Tale” is a study of contrasts: of blameless newborns linked with disease and impurity; of Barbieri, whose noble defense of Amalia stems from ambition and greed; of Count Isolani, a magnanimous Red Cross leader who, as president of the Bologna hospital board, is sued as a callous bigwig; of the poor wagging fingers at the rich, and most interestingly, of the way broad vectors of historical change find, in the fluid whole of lived experiences, a level of personal detail that is more concrete and yet less conclusive, its particularity based mainly in minor anecdotes and foggy emotions.

After catching syphilis from an infant who soon died, Amalia suffered for years through three phases of the usual symptoms, which began with a slew of lesions and gradually worsened into aches, fatigue, and dangerous organ troubles; survival was a matter of luck. Amalia’s own baby daughter was less lucky, and her quick death was only the first of a handful of futile pregnancies to follow. The case for Amalia’s compensation, which eventually reached the Supreme Court, focused on two slippery questions: Had the foundling in her care really been syphilitic from the start, and if so, whose fault was it that the foundling home, despite Amalia’s protests, didn’t recognize the early signs (such as blindness and spinal deformity)?

These questions were easier asked than answered. Syphilis can take months to show clear symptoms, and the cursory measures that foundling home doctors took to certify healthy babies routinely failed, especially in those earlier days of medicine. Nevertheless, before advances such as modern formula, pasteurization, and formula feeding, the only option was human milk, straight from the breast. A tough choice faced the hospital board: Breast-feeding more infants sooner meant hugely better survival rates, but it also meant more infected nurses — and now many of these were suing.

Throughout “Amalia’s Tale,” Mr. Kertzer, who is the provost of Brown University, hopes to seduce us into both an academic trust in his history and a story-time imagination of his characters’ inner lives. While Mr. Kertzer’s writing is energetic and his scholarship exhaustive, his attempt to give life to the long-buried cast is finally a Frankensteinian effort, the assembly resourceful but the stitching still awkwardly visible. Alongside meticulous research, Mr. Kertzer hazards not only explicit speculation (“Having no clear idea of where to go, she must have asked a woman nearby for directions”) but also a narrative omniscience (“He could not pass these markets without some feeling of dread, for times were not good”).

Difficulties aside, Mr. Kertzer is the best thing to happen to Amalia in about a hundred years. Eventually Baldieri won the case, but his legal expenses and related debts had grown so severe that Amalia and her infected husband Luigi were left with nothing but their convalescence. In this tale of reversals, it’s natural that Amalia’s winding return to dearth and obscurity has become, through Mr. Kertzer’s excavation, her only legacy.

Mr. Axelrod is assistant editor of Contemporary Poetry Review. He has contributed to Parnassus, New Partisan, and other publications.