We will start to-day with the subject of the digestibility of food. How can we estimate which food is easy to digest and which is not? When Beaumont had a patient with a gastric fistula, he thought he would find out about that. For at that time it was considered that the stomach was the main organ of digestion, and he thought that if food was found in the stomach after a long time it would indicate that the digestion of that food was not easy. On the other hand, he thought that if a certain article of food leaves the stomach in a short time, it would indicate that it was easy to digest. So, having this patient with a gastric fistula, he thought he would watch when the stomach emptied after certain articles of food, and he made out a scale of the digestibility of food accordingly.

In recent years, now that we are using the stomach tube so frequently, physicians do not need to have a patient with a fistula in order to watch the time when the food leaves the stomach, but can empty or wash out a stomach after a meal and examine its contents. This has been practiced by Leube, and later by Penzoldt. They took healthy individuals, medical students who were willing to take test meals and then have lavage practiced, or a tube introduced, to find out whether or not certain foods had left the stomach. Penzoldt has arranged a table showing what time certain articles of food require for digestion in the stomach.

Most physicians think that the shorter the time required for digestion in the stomach, the easier the digestion of that article. On further reflection, however, one can see that this is not a good gauge to go by. In reality, the main place for digestion is not the stomach, but the small intestine. The stomach prepares the food, but the actual digestion, for the greater part, takes place in the small intestine, and there the absorption occurs. Many substances leave the stomach without any change at all - the fatty 'substances, for instance. According to my experience, the main place for the digestion of meat is not the stomach but the intestine. The muscle fibers become swollen in the stomach, but they don't disappear. Connective tissue is one of the substances that are absorbed in the stomach. Then, we have some of the starchy substances which have already changed into sugar, which likewise are absorbed here. But everything else leaves the stomach, and enters the small intestine for further changes there. So the time the food remains in the stomach is not enough of a guide as to its digestibility.

Another plan of judging of the digestibility of food is to see whether it leaves a residue in the digestive apparatus or not - that is, whether it entirely disappears. If a certain article of food leaves a great deal of residue, and part of it passes through the entire digestive tract, it cannot be considered very digestible; while food that leaves no residue must be considered easy of digestion. So another scale has been made out according to that.

As a general rule, we can say that all animal food leaves less residue and is, in a way, more digestible than all vegetable food. All vegetable food leaves more residue, no matter what it is: seeds, nuts, etc., those vegetable foods rich in protein, that come in prepared forms flour, meal, - leave less residue than those materials which represent other vegetables, such as roots - like potatoes - or leaves and stems that contain a great deal of cellulose matter; also most foods that grow on trees contain a great deal of cellulose, which leaves a large amount of residue.

Of animal foods, it has been found that those meats that contain less fat are easier of digestion than those that contain a considerable amount of fat. For instance, pork takes a longer time in the stomach and also leaves more residue than beef; so you have another point on which to judge of the digestibility.

Another way of estimating the digestibility of food is by its physical character. All food before being absorbed must be changed into a liquid form. The organism cannot take up any substance unless it is in a gaseous or liquid form, or emulsified. Solid substances cannot penetrate the tissues. If we have to deal with foods that are liquid from the start, we can judge that their absorption will be much easier than that of solid substances which have to be changed into the liquid form. So you can make out a scale of the digestibility of foods according to their physical characteristics - whether or not they are easily changed into liquids. In this way we will have in that group which is more easily digested, or Group I, liquid food; milk, broths and gruels; eggs beaten up in milk - emulsified -are easy to digest; also beef juice - the juice pressed out from the meat. Group II; liquid at body temperature: fruit jellies and meat jellies, calves-foot jelly, ice cream that melts at body temperature, butter, all these are easily digested.

Group III

Foods that are easily broken up into fine particles beforehand, such as mashed potato; or where some mechanical movement is necessary to divide the food into fine particles, already prepared, mashed, etc., powdered meat, all mashed vegetables, purees; soft boiled and poached eggs belong to the same group; bread and crackers dried and pulverized, toast and bread cut up or ground up nicely and put into some liquid.

Group IV

Foods that are not easily broken up, but still change easily and do not present too much resistance to mechanical division, such as bread, boiled potatoes and vegetables not made into purees; foods such as sweetbreads, calves' brains, and fish are a little lighter than other kinds of meat, like chicken and chops, and are easier to mash up and chew.

Group V

Where the division is a little harder. Here we have the meats that have stronger fibers. Boiled lobster does not divide up so quickly as tender meat; fruits, where a great deal of chewing is required to break them up.

Group VI

This is the hardest group - salads, raw vegetables, cheese, and foods that contain a great deal of sulphur - such as cabbage, etc.

According to these lines you can see whether a food is easily digested or not, and if you act according to this scale you will see that it corresponds with the other scales mentioned before.