Baby cages were once an acceptable way for city-dwelling parents to let their children get some air. City apartments, as many people know, can be small and stuffy... in the late 19th century, the idea of actively "airing" your baby to promote health started cropping up in parenting books. The concept was introduced by Dr. Luther Emmett Holt who wrote about "airing" ... "Fresh air is required to renew and purify the blood, and this is just as necessary for health and growth as proper food," he wrote. "The appetite is improved, the digestion is better, the cheeks become red, and all signs of health are seen." In 1922, Emma Read of Spokane, Wash., applied for a patent ... "portable baby cage." ... Eleanor Roosevelt bought a chicken-wire cage in 1906 to hang out the window of her New York City townhouse on East 36th Street for her first child, Anna, to nap in—a practice for which her neighbors threatened to call the authorities on her.) It's not entirely clear when exactly the baby cage's popularity began to wane, but it likely had something to do with growing concerns for child safety in the second half of the 20th century.