The liver is commonly called the chemical work-shop of the body. The proteins and sugars are carried through the blood (portal veins) to the liver directly they are absorbed from the alimentary canal. As the food materials filter through the blood capillaries, between the liver cells, several substances are absorbed, particularly sugar, which is here changed into animal starch called glycogen. It is held in the liver for a few hours in the form of glycogen and then redigested by the action of an amylolitic ferment and again gradually given out into the blood in the form of sugar; hence sugar is subject first to the anabolic change of being built up into glycogen, and then to the catabolic change of oxidation and breaking down.
While the conversion of the sugar is one chief office of the liver, it also acts upon the proteins,—not as they are first passed through the liver in the blood, but as they are returned to the liver from the muscle tissue, partly oxidized and broken up into simpler products. The liver cells absorb and further oxidize and combine them into nitrogenous waste, which the kidneys throw off in urea.
The liver and the spleen also break up the pigment or coloring matter of the red blood corpuscles. As they become worn out, they are retired in the liver and the spleen from the circulation. The iron is retained by the liver cells and the remainder is thrown off from the liver, in the bile.
The liver is often called the watch dog of the body, because it is on guard for all poisons which pass through it in the blood. The large part of these toxic substances are absorbed through the alimentary canal with other foodstuffs. Many of them are the result of the fermentation of foods which are not digested as promptly as they should be, on account of an insufficient secretion of digestive juices, or a failure to secrete them in normal proportions, or due to inactivity of the stomach and intestines.
It surely is a wise provision of nature to supply a guard to oxidize, or break down these poisons and make them harmless, so that they do not pass to all parts of the body as poisons, thus affecting the nerves and the blood stream, and, through these, the entire system.
The necessity of correct habits of deep breathing will be readily seen, because oxygen is required to break down the poisons as well as to oxidize the waste of the system.
One example of the action of the liver in rendering substances harmless, is its oxidation of alcohol. From one to three ounces of alcohol a day are oxidized and made harmless in the liver, varying according to the individual and to the condition, at different times, in the same person. If the limit of one to three ounces is exceeded, the excess is not oxidized and intoxication results. These evidences of intoxication are in the nature of narcosis; alcohol is now regarded as a narcotic along with ether and chloroform.
It was formerly held by physiologists that alcohol was a food, because its oxidation liberates body heat and it was assumed that this liberation of heat, was the same as that freed by the combustion of fats, starches, and sugar uniting with oxygen. More recent knowledge, however, has unquestionably determined that heat, resulting from oxidation of alcohol, does not keep up body temperature; the pores of the skin are opened and there is a greater loss of heat through the skin. This really makes the system less able to resist cold. Large doses of alcohol actually cause a fall in body temperature and every force of the body is decreased in efficiency, while if alcohol were an actual food the efficiency would be increased. We are forced to the conclusion, therefore, that alcohol is a pseudo-food as it is a pseudo-stimulant.
Work of the Muscles