French physiologist Claude Bernard didn’t buy it. Bernard took some animals into the stomach. The year was 1855. The stomach belonged to a live dog and had been given a fistulous opening similar to the one that had enabled William Beaumont to spy on the digestive activities of Alexis St. Martin a few decades (and chapters) earlier. Bernard restrained the dog and then “introduced,” through the fistula, the hindquarters of a frog. After forty-five minutes, the frog’s legs were “largely digested”—nothing new to a Frenchman, except that here the frog was still alive. The experiment, concluded Bernard, “shows that life is not an obstacle to the actions of gastric juices.” And that cruelty was not an obstacle to the actions of Claude Bernard.*
In 1863, English physiologist Frederick W. Pavy extended Bernard’s findings to mammals. In keeping with the French market-day theme, Pavy selected a rabbit. He inserted one of its ears into the stomach of yet another fistulated dog while it was digesting a meal. Four hours later, a half inch of the tip was “almost completely removed, the small fragment only being left attached by a narrow shred to the remainder of the ear.” Again, digestion had proceeded unthwarted by the “living principle” or any sense of decency.
So Hunter was wrong. No vital force exists to protect a living being from the effects of the gastric secretions. Why is it, then, that stomachs don’t digest themselves? Why do one’s stomach juices handily digest haggis or tripe but not the very stomach that secretes them?
It’s something of a trick answer. In fact, stomachs can digest themselves. Gastric acid and pepsin digest the cells of the stomach’s protective layer, or mucosa, quite effectively. What no one in Hunter’s day realized is that the organ swiftly rebuilds what it breaks down. A healthy adult has a new stomach lining every three days. (More clever stomach tricks: key components of gastric acid are secreted separately, lest they ravage the cells that manufacture them.) The stomachs of John Hunter’s cadavers managed to burn holes in themselves because the mucosa-producing machinery shuts down at death. If someone dies in the midst of a meal—particularly in a warm clime, where weather stands in for body heat—the digestive juices continue to act though the restoration work has stopped.
If you must spend time in a digestive organ, I recommend the penguin stomach. Penguins can shut down digestion by lowering the temperature inside their stomach to the point where the gastric juices are no longer active. The stomach becomes a kind of cooler to carry home the fish they’ve caught for their young. Penguins’ hunting grounds may be several days’ journey from the nest. Without this handy refrigerated mode, the swallowed fish would be completely digested by the time the adults get back—“like going shopping and eating everything you bought on the way home,” as marine biologist Terrie Williams put it.
ONE REASON THE notion of living principle gained traction in John Hunter’s mind was that it offered a medical explanation for stomach snakes. As far back as Babylon and ancient Egypt, people had been coming to doctors with complaints of reptiles or amphibians living inside them. The malady hit an especially brisk stride in the late eighteenth century. “Thence it is,” wrote Hunter in his 1772 paper on the living principle, “that we find animals of various kinds living in the stomach, or even hatched and bred there.” Through the end of the century and likely beyond, biologists of imposing stature—not just Hunter, but also Carl Linnaeus—believed that frogs and snakes could live in humans as parasites, nourished by daily deliveries of swallowed food. Medical historian and author Jan Bondeson tracked down some five dozen case reports in medical journals from the seventeenth, eighteenth, and nineteenth centuries. Eighteen involved lizards or salamanders; seventeen posited snakes; fifteen claimed frogs; and twelve toads.
Despite the varied taxonomy and geography represented by these cases, the basic premise is more or less the same. The patient, vexed by odd sensations or pains in the abdomen, suddenly remembers a visit to the country. While walking home at night, the tale typically goes, he stops to drink from a pond—or marsh or rivulet or spring. It’s nighttime, and he cannot see what he is swallowing. Or he is drunk and does not notice. Sometimes he believes he swallowed eggs, other times the actual animal. In a few instances, the person lies down to sleep or passes out, whereupon some elongate, cold-blooded creature slithers down his esophagus and into his gut.
What cements the delusion, in the patient’s mind, is the timely sighting of an animal in the chamber pot. “When at stool, she had unusual pain in the rectum, and afterwards she thought she perceived something moving in the pot,” reads a typical case report, from 1813. Often the patient has been given a cathartic to relieve his symptoms. As here, in the 1865 case report of a stomach slug: “The patient had taken an injection per anum* . . . and immediately afterward something attracted his attention by moving about under his clothes.”