Does the meat we eat rot in the stomach?

This question was already answered more than two centuries ago, at the end of the 18th century, by an eccentric Italian scientist, Lazzaro Spallanzani. At the time, the leading theories were that the food fermented, putrefyed, or was ground into small pieces inside the stomach. Spallanzani was the first to carry out extensive observations on digestion within the living body of animals, himself among them.

He fed the birds with food in perforated containers that had a long piece of string. He would then remove the containers from the poor birds after a varying number of hours. From his results, he concluded that most of digestion is the solvent action of fluids in the stomach. He called these fluids "gastric juice".

To demonstrate the direct effect, he extracted a large amount of gastric juice from the birds' stomachs and placed chewed food in the juice and kept it at body temperature for three days. By repeated additions of gastric fluid, the food was completely dissolved.

Not satisfied with the results of the birds, he experimented on himself! He would place small bits of food inside small linen bags, sewing them up, swallowing them, and inspecting what came out the other end the next day. Sometimes he swallowed the half-digested meat a second or third time.

The linen bag passed through without causing any trouble and the contents were gone the next day. In another experiment, he waited three hours after swallowing a tube containing beef and vomited it back up, to prove that digestion occurs in the stomach, not the intestines. Finding that the meat had already softened, he confirmed his prediction. Apparently, even he was freaked out by this experiment and couldn't do it again.

The speed of the process suggested that the meat had not fermented or rotted, but had been dissolved by gastric juices through the cloth. We now know that Spallanzani was right: hydrochloric acid in gastric juice breaks down meat, and digestive enzymes break down proteins. Acidic gastric juice also kills bacteria, the agent behind "putrefaction." Proteins and fats are further broken down into amino acids and fatty acids in the small intestine and absorbed through the digestive wall into the bloodstream. There is nothing left to rot in the stomach.