No. 8.THE WAY WE DIGEST OUR FOODTHE STOMACHTHE LIVERTHE WAY THE FOOD IS POURED INTO THE BLOOD AND CARRIED OVER THE SYSTEM. "Good morning, Charles. Good morning, John. To-day we are to take a glance into our own stomachs, are we ?" "You don't mean literally, I suppose, but by some mysterious scientific investigation." "It has been done literally, in one case at least. However, let me tell you first what is known about the movements of the food after it passes into the body, and then perhaps I c-M give you some idea of the iiiode in which the facts have been learned. The stomach is a bag, lying pretty nearly across the middle of the body, a little to the left, of a size sufficient to hold about a quart. As the food is swallowed it passes through a long, flexible, moist tube, called the esophagus, and falls into the stomach. The presence of food in the stomach stimuliites the gastric glands to secrete the gastric ? juice. These glands are situated in the inner coating of the stomach, they are very numerous and exceedingly small. The gastric juice which they secrete partially dissolves the food, converting it into a semifluid mass, called chyme. In order to mix the gastric juice thoroughly with the food, the stomach has aii instinctive movement which carries its contents along its greater curve and returns them by the lesser, mixing them by .a churning motion, occupying about three minutes in each revolution. Thus the food is frequently presented to the passage from the stomach in the duodenum, and, by one of the most wonderful of all the mysterious adjustments that we find in the operation of the human system, as soon as any portion of the food which is thoroughly digested presents itself to this passage, the passage opens and allows the chyme to flow out into the duodenum. When food not perfectly digested is presented, the passage refuses to open, and thus the food is retained in the stomach until all of it that can be converted into chyme is so converted. After indigestible matter has been presented several times to t he pyloric orifice and returned to the stomach, the passage finally opens, and all the contents of the stomach flow out in to the duodenum." " How does this passage know whether the food is digested or iiot." " That is another of those questions which it is easy to ask but impossible to answer. Nobody knows." "Well, how do they know that these motions do take place ?" " Some years ago a soldier in Canada was wounded in the stomach by a bayonet, and when the wonnd healed, it left an opening into his stomach by which 'persons could look in and see the operations of digestion going on. Dr. Beaumont, of St. Louis, took this soldier, St. Martin, under his care, and made Ii long series of investigations of the process of digestion. He had a little silver ladle made, and used to dip out the gastric juice and try its action on meat and other substances outside of the body. But with this wonderful opportunity lie did not discover much which had not been previously known, a fact which proves, in a very striking manner, the thoroughness of the physiological investigations which had been made before." " We will believe your statements, then. What takes place next ? "The proper way is to receive the present conclusions of science till you acquire sufficient knowledge of the subject to test them for yourselves. You will find that it will take very careful and laborious experiments to disturb these- conclusions. After the chyme has passed into the duodenum, it is mixed with two other fluids, which dissolve it further and convert it into a milky liquid called chyle. These two fluids that mix with the chyme are the bile, which is secreted by the liver, and the pancreatic juice, which is . formed by the pancreas. From the duodenum, the chyle, mixed with the was te indigestible portions of the food, passes - on through the jej un um into the small intestines, which, in man, are abont 15 feet long, and are folded back and forth in the lower part of the abdomen. This is the gut which; in the hOlt, is used for making sausages ; being air tigh t, it preserves the meat which'is stuffed into it from decay. Along the smal intestines .are ^mner^us mouths which lead into very small tubes or ducts, by which the chyle is sucked in, as it flows along through the intestine, and these tubes meet, like the branches of a river, till they form one large. pipe or duct, which leads up by the side of the back bone carrying up the chyle and emptying it into a large vein in the left side of the neck, by which it is borne directly to the heart and distributed over the system. The little tubes which suck up the chyle from the intestine called lacteals, and they have the power of rejecting the undigested waste matter, which accordingly continues on its course, passmg through the colon, up the right side, across the body just under the stomach, down the left side, and out by the rectum." "I thought you were going to tell us aboutthe action of carbonic acid in our bodies." " I was, but thought it best that you should have first a general notion of the mode in which nourishment is supplied to the system. I will next explain to you the way in wilich a portion of this food is used as fuel to heat our bodies, but as this will take some time, we will postpone it till next Saturday."
This article was originally published with the title "Talk with the Boys" in Scientific American 3, 24new, 374 (December 1860)