PUKING FOR SCIENCE

DOI: 10.4324/9781003239284-6

Lazzaro Spallanzani was always curious. He wondered how language was created, and how nature worked. Why could salamanders and tadpoles regrow their tails, but cats could not? Where did springs and fountains come from? How do plants grow? And what happens to food when people eat it?

In the mid-1700s, there were no X-rays. Nobody had invented microscopic cameras or ultrasound. The only way for a scientist to see inside a body was to cut it open, and there really weren’t many volunteers for that. Spallanzani realized that when it came to studying human digestion, he was going to have to use himself as the test subject.

As a professor of natural history, Spallanzani was famous for his daring experiments. He had climbed the Italian mountains to prove that snowmelt contributed to springs and rivers. He had figured out how to aim sunbeams at salamanders so he could see their blood flow through a microscope, and he had experimented with animals and their digestive systems.

Spallanzani had fed glass balls to chickens and turkeys and learned that their powerful grinding gizzard could turn the glass into sand in just a few hours. He created tin tubes with small holes punctured in them, so he could learn what happened to food that was eaten by animals. He wanted to see if the juices in the stomach dissolved the food or if it was ground up like in birds.

After he filled the tube with food, Spallanzani poked the tube down the animal’s throat and waited for it to be expelled in the animal’s manure. Then he fished the tube out of the animal dung and opened the tube to see what was left inside.

Spallanzani had fed glass balls to chickens and turkeys and learned that their powerful grinding gizzard could turn the glass into sand in just a few hours.

Getting the animals to swallow the tubes was not easy. He was attacked by birds when they fought back and was bitten by both dogs and snakes. Spallanzani knew it would be even more difficult to get a human to cooperate with the experiment, so he tested himself.

He started his human digestive experiments by chewing a piece of bread and spitting it back out. He took the chewed-up bread and put it into a small linen sack. He sewed the sack shut and then swallowed it. About 23 hours later, Spallanzani fished the sack out of his own fecal matter. He found that the sack was not damaged in any way, but the bread had vanished.

Since he hadn’t had any digestive issues swallowing the bag of bread, he decided to go ahead with more experiments. Spallanzani carved tiny capsules out of wood. Like the tin tubes he used on animals, these had holes that allowed the digestive juices to reach the food inside. If the food disappeared in the wood capsules, this would tell Spallanzani that food was being dissolved by digestive juices rather than by the smashing action of the stomach.

Once again, he found the capsule came out the other end of his body in about 23 hours. The capsule was whole and had not been damaged, but the food inside had dissolved. Food was being digested by the juices in the stomach. It was the first scientific proof of how human digestion worked.

But Spallanzani wasn’t done experimenting. He was still curious. What could the stomach juices dissolve? He filled the capsules with tough meat and gristle. He had to dig that capsule out of his fecal matter and reswallow it three times before the gristly meat disappeared, but eventually the stomach juices did dissolve it.

Then, he tried a piece of bone. Even after he swallowed and digested it several times, the bone did not dissolve. He decided that humans should avoid eating bones.

Next, he wanted to try experiments with the gastric juices outside of the body. He had gotten gastric juice from animals by forcing them to swallow a sponge and then pulling the sponge back up. He wrung the juice out of the sponge.

He tried the same experiment on himself, but he could only swallow two sponges at a time and they didn’t soak up enough liquid for him to experiment with. Finally, he decided to try vomit.

He woke up early in the morning, when he was sure his stomach was empty, and stuck his finger far down his throat. This caused an automatic gag response and he threw up gastric juice. He used this juice in several experiments and learned that gastric juice would reduce a piece of meat to slime in just 3 days.

Because of Spallanzani’s experiments, scientists understood for the first time that humans grind their food with their teeth, but there is no more grinding done once food is swallowed. The rest of the digestive process is completed through chemical reactions.

His experiments in digestion ended in about 1778, but that was by no means the end of his scientific career. Spallanzani kept experimenting the rest of his life. He tested the theories of regeneration by cutting off the tails of salamanders and tadpoles and observing how they grew back. He studied the speed of lava flowing on Mount Vesuvius. He passed out from inhaling poisonous gasses on Mount Etna. He also experimented with the theories of spontaneous generation and helped prove that animals did not magically arise from dirt or water.

Then, he tried a piece of bone. Even after he swallowed and digested it several times, the bone did not dissolve. Ele decided that humans should avoid eating bones.

When he died at the age of 70, his brother had Spallanzanis heart removed, preserved in a marble jar, and donated it to his hometown parish. Spallanzani died of a bladder disease, so his brother also had the bladder preserved and gave it to the historical museum at the University of Pavia.