The liver is the great chemical laboratory of the body. A very large part of the chemical work done in the body is accomplished in the liver. As mentioned above, the liver receives from the portal vein blood containing the just-absorbed proteins and sugars from the alimentary canal. These food materials are distributed to the liver cells, and as they slowly filter through the blood capillaries between the cells within the lobules of the liver, the liver cells, which lie along the capillaries, absorb several substances, among them sugar. An important part of the work of the liver is to absorb sugar from the blood and change it into animal starch or glycogen. This process is called glycogenesis. While glycogen possesses the same chemical formula as starch [(C6H40O5)n ], it is evidently not absolutely identical with starch in its molecular structure. However, it is insoluble in water, and the evident purpose of the formation is to take sugar out of circulation and store it in the condition of starch. After glycogen has been held in the liver cells for a few hours it is gradually given out again in the form of sugar. In order to change the glycogen to sugar, it must be redigested, and the steps of this redigestion is called glycolysis. To produce this change the liver possesses an amylolytic ferment. The process of glycogenesis is an anabolic one, while glycolysis is a catabolic process.

Another important function of the liver has to do with the proteins. While these are probably unchanged in their first passage through the liver, when they come back from active tissues, particularly from the muscle tissues, partly oxidized and broken up into simpler mid-products, the liver cells absorb these mid-products of protein catabolism, and further oxidize and combine them into the nitrogenous excreta, which will be later thrown out of the body by way of the kidneys.

Mention was made above, when we were describing the bile, of the bile pigments. These bile pigments arise from the decomposition of hemoglobin in the liver. Hemoglobin is red pigment of the red blood corpuscles. As these corpuscles become decrepit and useless they are retired from the circulation, and are caught either by the spleen or by the liver, and broken up into simpler elements. Incident to this breaking up of the hemoglobin, the iron is retained by the liver cells, while the remaining portion oxidized to the condition bilirubin and biliverdin is thrown out of the system as a constituent of the bile. This particular constituent of the bile is purely excretory, as no one has found that it serves any purpose in the digestion or absorption of food.

Another important service performed by the liver is the oxidation of toxic substances which come to it in the blood. No small part of these toxic substances comes in the portal blood, having been absorbed from the alimentary canal along with the food. Many of these toxic substances have resulted from bacterial fermentation of foods, some from the excessive proteolysis produced by trypsin when the peptone is not at once absorbed. Toxic substances finding their way accidentally into the alimentary canal along with the foods may be thus oxidized in the liver. This oxidation of toxic substances in the liver is one of the most important protective measures devised for the animal body. Among the numerous ferments in the liver are the oxidases. It is these oxidases that bring about the oxidation of the toxic substances, which oxidation, changing the substances to simpler forms, makes them harmless. A notable example of this wonderful action only recently discovered through laboratory researches is the protective oxidation of alcohol in the liver. Up to the limit of one to three ounces of alcohol in twenty-four hours, the limit varying with different individuals under different conditions, the liver is able to oxidize and does oxidize the alcohol, thus reducing it to a harmless condition. Of all the toxic substances thus oxidized in the liver, it is probable that alcohol can be oxidized in the largest quantities. When alcohol is ingested in quantities not exceeding the physiological limit above mentioned, it is all quickly oxidized as above described. Being thus early caught in the liver, it does not exert its toxic effect upon the system. If a larger amount than above mentioned, that is, if the physiological limit is exceeded, then evidences of intoxication make themselves manifest in degree proportional to the amount taken over and above the physiological limit. These evidences of intoxication, when critically studied, are all found to be in the line of a narcosis. So alcohol has come to be looked upon as a narcotic along with ether and chloroform.

Incident to the oxidation of alcohol in the liver, two things happen that have been widely misunderstood and misinterpreted by physiologists and clinicians. In the first place, this oxidation naturally and necessarily liberates heat energy, thus increasing the sum total of body heat. Second, the oxidation of this carbonaceous substance increases the output of carbon-dioxid gas. Metabolism experiments naturally show that where alcohol has been incorporated with the foods, especially when the physiological limit is not exceeded, body heat has been increased and the carbonaceous output as represented by the C02 collected is greater in proportion to the consumption of fatty reserves of the body and fats of the food, than is the case when no alcohol is given. So this oxidation was easily and naturally assumed to be analogous, if not actually equivalent, to the oxidation of fats, or sugars, or starches. That being admitted, alcohol was naturally looked upon as a food. In the light of recent researches on the action of alcohol in the liver, these results, which looked so plausible a decade ago, are subject to a very different interpretation: that heat resulting from this protective oxidation is not available for maintenance of body temperature. This is evident from the fact, very generally admitted and universally known, that alcohol, in any quantity small or great, not only fails to protect the system from extreme temperatures, but actually makes the system less resistant to low temperature. Larger doses will cause an actual fall of temperature when the individual is subjected to low temperature soon after taking the larger quantity.

When we find that no function of the body is made more efficient or in any way improved by alcohol, but that all functions which are modified at all are distinctively decreased in efficiency by the ingestion of appreciable doses of alcohol, it must be evident that the old theory that this substance possesses a food value will have to give way to the more rational theory based upon recent researches that this substance is a pseudo-food as it has proven to be a pseudo-stimulant.