A nondescript, white apartment building near Lake Street in Minneapolis once housed an amusement park "infantorium," where people paid a dime to view premature babies in glass incubators in the early 1900s.

Part freak show, part pioneering neonatal hospital, the brick structure at 31st Avenue S. and 31st Street is all that's left of Wonderland — a 10-acre amusement park that featured a giant log flume and a 45-mph roller coaster from 1905 to 1911.

The tiny babies proved to be just as popular a draw.

"The cutest little packages you ever saw … like bonbons," a 1905 Minneapolis Tribune article began, calling the infants "little morsels of humanity … tucked up cozy and warm in little glass castles."

Born two to three months early, the babies were fed only breast milk and kept in seven newfangled incubators until they reached 6 pounds and moved to a nursery and eventually, back to their families. At the time, hospitals considered such preemies unwanted "weaklings" — barring them from admission.

"There really wasn't better care available," Minneapolis historical researcher Katie Thornton said. "No one in the medical community was standing up for them."

Thornton, 27, grew up in south Minneapolis and returned home after studying American history at Oberlin College in Ohio. She learned about incubator sideshows while scouring digitized newspapers for a college research paper on Wonderland and the broader role early 20th-century amusement parks played among newly urbanized working classes. Earning a Fulbright-National Geographic fellowship for digital storytelling, Thornton successfully pitched a 39-minute podcast on the infantoriums to 99% Visible — a popular Oakland-based podcast.

For those who think historic storytelling is limited to dusty old books, yellowed newspaper clippings and spools of microfilm, check out Thornton's new-age approach. In addition to her podcast at 99percentinvisible.org/episode/the-infantorium, she regularly posts archival images on her public Instagram page at instagram.com/itskatiethornton.

"There's something deeply unsettling to modern eyes about the whole concept of incubator sideshows," she said. "Today, it's clear that putting babies on display and profiting off of them is exploitative."

Minneapolis was far from alone with its preemie freak show. The 1901 World's Fair in Buffalo featured a 10-cent incubator show on its Midway. Chicago, Denver and Minneapolis joined the craze in 1905. And New York's Coney Island sold tickets to view preemies into the 1940s.

Thornton's research winds back to the advent of incubators in France, where doctors borrowed the idea from the poultry industry, which used incubators to hatch chicken eggs. "Basically, it was a warm box, heated by a hot water tank below," she said.

That 1905 newspaper story carefully explained how the air was sterilized, ventilated and regulated to control humidity: "The baby mattress is laid on a wire netting, which separates the living apartment of his glass house from the little heating plant and water tank below."

The idea to place premature babies behind incubators' glass windows started in 1896 in Germany as Die Kinder-Brutanstalt, which translates to "child hatchery."

"It took on the environment of a sideshow," said Dawn Raffel, author of a new book called "The Strange Case of Dr. Couney: How a Mysterious European Showman Saved Thousands of American Babies."

Martin Couney debuted his incubator baby show in London in 1897 and brought the idea across the Atlantic the next year for the Trans-Mississippi Exposition in Omaha. A bit of a charlatan, Couney professed to be a European-trained doctor, but researchers have been unable to find any medical licenses.

He became rich displaying premature infants alongside sword swallowers and bearded ladies on midways in Coney Island, Atlantic City, Minneapolis and other spots. But Couney died penniless after hospitals finally made his sideshows obsolete in the 1930s.

Decades earlier, Couney tried to donate his incubators to local hospitals, but no one wanted them. Was he a fraud who exploited tiny babies? Sure. But he was likewise considered a hero by mothers who went into to labor months early. Before his sideshows, those infants were doomed.

"The doctors … felt that the babies were weaklings … and nobody made any great effort to save them," said Beth Allen, 78, a Brooklyn native who spent her early days in a Couney sideshow and whom Thornton tracked down for her podcast.

"The babies in his care were more than four times as likely to survive into childhood," Thornton said. "He took in babies of all races and classes, and he never once charged the families. Everything was funded by admissions."

And it all played out amid the din of roller coasters at amusements parks and fairs — including that white apartment building in Minneapolis's Longfellow neighborhood that once housed Wonderland's Infant Incubator Institute, or Infantorium.

"The incubator building is in reality a splendidly equipped hospital for babies, immaturely born," the newspaper said in 1905. "It is not a museum or mirth-provoking feature as are the other entertaining devices in Wonderland."

Curt Brown's tales about Minnesota's history appear each Sunday. Readers can send him ideas and suggestions at mnhistory@startribune.com. His latest book looks at 1918 Minnesota, when flu, war and fires converged: http://strib.mn/MN1918.