production of glycogen in the body. Certain substances known as galactosides, which are combinations of galactose and some substances other than carbohydrates, are found in the nerve and brain tissues of the animal body.

Disaccharides.—Of the second group of carbohydrates, we are probably more familiar with sucrose, or cane sugar, than with either of the other two, since it is in this form that the greater part of the sugar eaten is purchased.

Sucrose.—By far the greater part of the sugar entering into the average dietary is manufactured from sugar and sorghum canes, and from sugar beets; but appreciable quantities are derived from the sugar maple and sugar palms. Many of the sweet fruits are rich in this form of sugar; pineapples are said to contain at least half of their solids in sucrose; and although other fruits and vegetables do not contain so high a percentage of this sugar, oranges, peaches, apricots, dates, raisins, prunes, carrots and sweet potatoes contain goodly quantities, which are associated with glucose and fructose. Sucrose is readily hydrolized, either by acids or enzymes. The inverting enzyme (invertase) of yeast and sucrase of the intestinal juice, convert sucrose to fructose and glucose, in which forms it is absorbed into the portal blood. It is believed that when sucrose is eaten in very large quantities, it is sometimes absorbed from the stomach. In these cases it does not become available for use in the body, but acts in the same manner as when injected directly into the blood stream, being excreted unchanged by way of the kidneys. According to Herter, sucrose is much more susceptible to fermentation in the stomach than either maltose or lactose; and since it has no advantage over these sugars from a standpoint of nutrition, they are frequently substituted for sucrose in cases where the dangers arising from fermentation must be avoided.

Maltose (Malt sugar) is an important constituent of germinating grains—malt and malt products being formed as the result of enzymic action (amylases) on starch. A similar action takes place in the mouth as the result of the ptyalin in the salivary juices and in the intestines from the action of the starch-splitting enzyme, amylopsin, in the pancreatic juice. The maltose thus formed is further converted into glucose by the sugar-splitting enzyme in the intestinal juice, and in this form it is chiefly absorbed. Maltose is also an intermediate product formed during the manufacture of commercial glucose as the result of the boiling of starch with dilute acids.

Lactose (sugar of milk) is one of the most important constituents in the milk of all mammals. In freshly secreted human milk, lactose occurs in quantities ranging from 6 to 7%, and in the milk of cows and goats from 4 to 5%. Lactose is much less soluble than sucrose, and decidedly less sweet; hence, owing to this latter property, as well as to its lack of susceptibility to fermentation, lactose is frequently used to bring up the sugar content of infant formulas to the desired percentage, and the diets used in the abnormal conditions when additional energy material is needed. During the process of digestion, lactose is hydrolized by the lactase in the intestinal juice, yielding one molecule of glucose and one of galactose. Like maltose, little if any of this sugar is absorbed in its original form, since experiments made with injections of lactose into the blood result in the rapid and almost complete elimination by way of the kidneys. No such results are obtained when even large amounts of lactose are taken by way of the mouth.

Polysaccharides.—This group of carbohydrates is complex in character, built up of many sugar molecules, and upon digestion must be broken down into simple sugars before they can be utilized by the body.

Starch is the form in which the plant stores her supply of carbohydrates. It is found in this form in roots and (mature) tubers, three-fourths of the bulk of which is made up of this material. From one-half to three-quarters of the solids of grains is made up of starch also. Pure starch is a fine white powder, odorless and almost tasteless. It is insoluble in cold water and alcohol, but changes from an insoluble substance to a more soluble one upon the application of heat. Upon hydrolysis starch gives first a mixture of dextrin and maltose, then glucose alone as an end-product. This hydrolysis may be the result of enzymic action, as occurs upon bringing starch in contact with the ptyalin in the saliva, or with the amylopsin in the pancreatic juice; or it may be the result of boiling starch with acid, as is seen in the manufacture of commercial glucose.

Dextrin, as has already been stated, is an intermediate product of the hydrolysis of starch by acid or enzymes.

Glycogen is the form in which the carbohydrates are stored in the body, just as starch is the form in which they are stored in plants. It is found in all parts of the body, but is especially abundant in the liver. Here it is stored in the cell substance rather than in the nucleus. The storage of glycogen in the human body depends largely upon the mode of life and upon the diet. Active muscular work, especially out of doors, uses up the store of glycogen with great rapidity; while rest and a sedentary life promotes its storage. The body readily converts its supply of glycogen into glucose, the form in which the body uses the carbohydrates for fuel.

Cellulose is a woody, fibrous material insoluble in water and to a certain extent impervious to the action of the digestive enzymes. This carbohydrate constitutes the skeleton of plants just as the bones constitute that of the animal body. It is probable that owing to the length of time required for this carbohydrate to be broken down in digestion, much of it escapes oxidation entirely. Hence, it passes down the digestive tract lending bulk to the food mass and thus promoting peristalsis throughout the whole of the digestive tract.

Organic Acids.—Certain of the carbohydrate foods (fruits and green vegetables) contain appreciable amounts of organic acids or their salts; oranges and lemons, for example, are rich in citric acid; grapes contain considerable quantities of potassium acid tartrate, apples and other fruits have malic acid; many of the fruits have succinic acid; a few foods contain oxalic acid, or oxalates. All of these organic acids are burned in the body to produce energy, with the possible exception of the oxalates, which seem to have little, if any, food value. According to Sherman, these organic acids have a lower fuel value, per gram, than carbohydrates, but are reckoned as such in computing a food in which they exist. The function of these acids is chiefly that of neutralizing the acids formed in the body in metabolism. Being base-forming in character, they function after absorption and oxidation in the body as potential bases—the base associated with the acid in their ash combining with carbonic acid to form carbonates, which act as above described.

Bacterial Action upon Carbohydrates of Foods.—The bacteria that act chiefly upon the carbohydrates belong to the fermentative type. The substances formed as a result of this activity are certain acids—lactic, butyric, formic, acetic, oxalic, and possibly alcohol. Certain forms of carbohydrates are more susceptible to bacterial fermentation than others. Herter claims that sucrose and glucose are much more so than lactose, maltose, or starch. The substances thus formed through bacterial activity are not believed to be toxic in character, but merely irritating. However, the irritation arising from excessive fermentation in the