The intimate connection between the gall bladder, the liver, and the organs of digestion, brings about many complications; and a diagnosis as to whether or not a person is suffering from gall bladder inflammation, or from an infected appendix, or from ulcers of the stomach, or from several other conditions, involves the use of many new and delicate tests, as well as a great deal of knowledge concerning the manifestations of the various diseases concerned.

In an earlier day the physician was compelled to base his examination of the condition of the gall bladder on what he could feel with his finger beneath the edge of the ribs. He still employs this measure; but, in addition, he is likely to make X-ray pictures to see if there are stones in the gall bladder; to inject substances which localize in the gall bladder and help to make it visible to the X-ray; to pass a tube through the stomach into the small intestines and to take out some of the bile for study; to examine the excretions of the body as to their content of bile and of bile salts; and to study the blood as to any changes which it may have undergone because of difficulties of excretion and secretion of bile.

Diseases of the liver involve gross changes in the organ due to inflammation, infection, poisoning by various metals which affect the liver particularly, hardening of the liver due to the effect of alcohol or changes brought about by food poisons, tumors of the liver, infection by tuberculosis or some of the venereal disorders. Since the liver is so intimately bound with the digestion and with the creation and maintenance of the blood, extensive studies of the blood and of the various secretions and excretions are necessary to make an exact diagnosis.

In the days when men used to drink tremendous quantities of alcoholic liquors day after day, cirrhosis or hardening of the liver with the development of hobnail surfaces was an extremely common complaint. As times and conditions have changed, this condition is seen more and more rarely.

On the other hand, modern industry has introduced the use of chemical substances of a poisonous nature which frequently manifest their first serious effects on the human being by producing changes in the tissue of the liver and correspondingly prompt changes in the blood. Scientific investigators study these problems not only by chemical and physical studies of the human body, of the blood, and other fluids, but also by careful examination of the organs after death in cases in which fatalities have resulted from poisoning. In such instances the use of the microscope may show great changes in the blood cells that pass through the liver. The very tissue of the liver itself may have disappeared and have been substituted by fat. The metallic substances may be found in the cells of the organ itself. As a result of these studies, it becomes possible to plan methods of treatment that serve to relieve the symptoms, to save lives, and to extend the advance of knowledge still further into the realm of the unknown.

Metabolism. Before the coming of the modern era, the physician had no way of knowing exactly how well the vital organs of his patient actually were functioning. When it began to be realized that the body is a great physiochemical mechanism in which all sorts of reactions are going on, means were developed for measuring the rate of speed of these reactions and their functional efficiency. Everything that takes place in the human body is, to some extent, the result of a chemical change. Whenever any organ performs its duties, energy is used and is transformed into some equivalent of a different character. Energy comes from food. When the food is taken into the body, it is broken up into fundamental constituents which are taken up by various organs and transformed into compounds which the body can use. The sum of all these activities is the basal metabolism, which is influenced by many factors.

Formerly the value of all foods was expressed wholly as energy value, or caloric value. It was calculated that one gram of protein would provide about four calories, as would also one gram of carbohydrates. However, one gram of fat, which is more productive of energy than protein or carbohydrate, provides nine calories. It may therefore be seen how small a quantity of food is necessary to produce four calories and why it is that butter and fats help to put on weight so rapidly. Naturally, a person doing a small amount of work does not need to take in so many calories as one doing heavy labor. Whereas a clerical worker eats from 2,500 to 3,000 calories per day, a stevedore or woodchopper consumes from 4,500 to 6,000, and a lumberman may take as much as 8,000. In the same way, a seamstress takes from 2,000 to 2,300 calories, whereas a maid-of-all-work or a laundress consumes 2,800 to 3,500.

End Products of Digestion. Although much is known as to what happens to the foods when taken into the body, many additional investigations must be made before the complete story of the digestive chemistry is told.

Proteins break down into amino-acids and are circulated in the blood in this form. Some of these products are again put together to make body proteins, later to be broken down a second time under the influence of various conditions in health and disease. Some of the protein is changed into urea and can be found in the urine in this form. In certain diseases some of the products of digestion and body chemistry, which ordinarily are changed for various purposes within the body, are excreted unchanged; and these have been studied by the physiological chemist. By such studies it has been found, for example, that there are forms of sugar which may be excreted and which will give all of the ordinary tests for sugar, and yet prove not to be the particular sugar which is associated with diabetes.