After the food leaves the stomach, it is acted on by several digestive enzymes. Some of these are secreted by glands located, like the stomach glands, in the wall of the intestine. But the most powerful digestive juices of all are those secreted by the pancreas and poured into the intestine in its upper part. One of the pancreatic enzymes, trypsin, is a rapid and powerful split-ter of the protein foods. Another, lipase, splits fats into simpler absorbable compounds. The third, amylase, resembles the salivary secretion, ptyalin, in that it breaks down complex starches and sugars into simpler chemical forms. The pancreatic secretion mixes with the food, as has been said, at the upper part of the small intestine.

The stomach empties itself in about four hours. The food, in various states of digestion, is then carried forward by the intestinal peristalsis, which is much like the constrictive movement of the stomach. It is carried forward at a rate allowing time for the intermixture of intestinal, pancreatic, and liver juices, for the conversion of food into assimilable form, and for absorption, through the intestinal walls, into the blood. Finally, through the ileo-ca2cal valve, it reaches the large intestine, where absorption, except for water, largely ceases and the waste products are agglutinated with the mucous, bacteria, and epithelial debris from the entire intestinal tract in the form of faeces, a stool or mould of which is evacuated from the body by the act of defecation once, according to the immutable standard of modern civilization, in every twenty-four hours.

The digestive system may be conceived in its simplest form as a muscular tube into which glands all along its course pour secretions. Some of these glands are embedded in the wall of the tube ; some, such as the pancreas and the liver, are so large that they lie outside and discharge their secretion through a duct which empties into the digestive canal. The muscular action of the walls of the canal pushes the food ever onward.

Fortunately about this time an Indian got shot. On June 6, 1822, to be exact, at Mackinac. His name, which will be floating on the surface of the river of time when every poet and columnist now living shall long have been forgotten, was Alexis St. Martin. The accidental discharge of a shot-gun in the trader’s store of that frontier post tore off the skin and muscles in the upper part of St. Martin’s abdomen and the outer layer of the wall of his stomach.

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.