After the revival of learning men began to become interested in certain apparently spontaneous changes which occurred in substances left alone in nature. For instance, why does meat get corrupted? Why do maggots swarm in it? Why does milk sour? Why does grape-juice turn into wine? Why does apple-juice turn into vinegar? Finally, why does food undergo a change in the stomach? All of these changes seemed to them to be of the same nature. They were all thought to be due to “spontaneous generation.” Meat changed, maggots swarmed, milk soured, food digested – by the act of spontaneous generation or spontaneous metamorphosis.
An Italian, Francesco Redi, undertook to answer the question about the maggots. The learning of the time was certain that they developed spontaneously in the meat. He put pieces of meat into open jars, and other pieces of meat into jars over which he placed parchment and wire-gauze. The maggots developed in the meat in the open jars; they did not develop in the meat in the covered jars, but maggots grew on top of the wire-gauze or on the parchment covering the jars. The idea of spontaneous generation began to fade. What did it mean anyway?
A Frenchman, Reaumur, had a pet kite. He got some of the juice from its stomach and showed that this juice dissolved food in a glass. Another Italian, an abbe – Lazaro Spallanzani – said that Reaumur was right not only about birds, but also about human stomach-juice: it seemed to melt food away. The significance of this, to the learning of the time, was that the stomach juices would convert or digest food even when they were outside the stomach: the supposed “vital” influence of the stomach was unnecessary. The abbe also found that saliva would change certain (starchy) foods even in a bottle. This was in 1782.
Ensued argument. Hunter, the Great Cham of medicine in England, bellowed
Some Physiologists will have it that the stomach is a Mill; others that it is a fermenting Vat; others again that it is a Stew Pan; but in my view of the matter it is neither a Mill, a fermenting Vat, nor a Stew Pan – but a Stomach, gentlemen, a Stomach.
As no one knew what he meant, he acquired a great reputation.
Matters were not much clarified after all, for fifty years later, in 1825, a New York intellectual by the name of Nathan R. Smith could say, and be applauded, that :
…the properties of the gastric juice suggested to the older anatomists the idea that a myriad of small worms attack the food which was swallowed and reduced it to a uniform pulpy mass.”
He believed that they were as near the truth as those:
…who consider the process to be performed by a chemical agent.