canal of man it resists the action of ptyalin and amylopsin, but undergoes partial decomposition under the influence of bacterial enzymes with the production of methane and carbon dioxid.

Inulin (C38H62031) is a starch-like substance in solution in the sap sap of many plants, but especially in tubers of dahlia, Jerusalem artichoke and potato, roots of chicory, dandelion and lichens. It is obtainable from these sources as a white powder consisting of spheroidal crystals, soluble in hot water, sparingly soluble in cold water. It stands in the same relation to levulose as starch does to dextrose. Inulin is not readily acted upon by the enzymes; diastase has little influence over it; ptyalin and amylopsin do not convert it into sugar; it is, however, converted into sugar by the action of dilute acids and is probably digested. Although inulin is readily hydrolyzed to levulose by acids, it is not attacked by the saliva or pancreatic juice. Sandmeyer (11), after feeding 80 grams of inulin to a diabetic dog, recovered 46 grams in the feces, and Mendel and Nakaseko (12) found that little if any glycogen resulted from feeding inulin to a rabbit. Mendel and Mitchell (13) injected inulin in the peritoneum of a rabbit and recovered most of it in the urine.

Pectose Bodies are found in most fruits, in a few roots, and in some vegetables. They are peculiar substances which under certain conditions cause fruit juices to gelatinize. Their constitution and composition cannot very well be ascertained because they cannot be separated from the associated cellulose without disorganizing them or changing their substance. The subject has been treated at some length in Chapters XI and XIII, to which the reader is referred. Pectose is insoluble in water, alcohol and ether, but it is converted by the digestive juices and acids into pectin, which is soluble in water. Pectin is the chief substance in fruit and vegetable jellies. The nutritive value of pectin and pectose bodies is probably about the same as that of starch. The pectins are considered by some authorities to bear the same relation to pentoses as dextrins do to hexoses.

HYDROCARBONS

Hydrocarbon derivatives of various kinds occur in foodstuffs. They contain carbon, hydrogen, usually some oxygen, but ordinarily no nitrogen, phosphorus or sulphur as essential ingredients, though, as we shall see, they enter into various combinations with compounds of these elements. The amount of oxygen in the fats which make up an important portion of this group is relatively small, leaving their combining capacity with oxygen high. This fact gives them a fuel value double that of

either proteins or carbohydrates and enables them to supply a correspondingly large energy value to the animal economy.

Classification of Hydrocarbons.-Hydrocarbon derivatives form the bulk of fat, butter, suet, oils and other fatty substances. While carbohydrates are chemically hydrocarbon derivatives, their distinctive chemical composition and their physiological importance render it convenient to describe them as a distinct group.

TERPENES.-Relatively few of the compounds of carbon and hydrogen without oxygen appear in foods. Among the volatile or essential oils, however, are found a number of terpenes of the composition C10H16. These include d-limonene, in lemon, kümmel (caraway), dill and celery; a- and g-terpinenes in cardamon; phellandrene in fennel; carvone in kümmel and dill; and camphene in ginger.

ALCOHOLS.- When one or more of the H atoms of the hydrocarbon molecule is replaced by OH radicals, we have an alcohol, the particular alcohol being determined by the nature of the original hydrocarbon, as well as the number and position of the replacing hydroxyls. Ethyl alcohol (C2H2OH) occurs in small quantities in muscle and other organic substances, but is chiefly the product of alcoholic fermentation of sugars.

It has been well said that the chief effect of food is nutritive, while the most important action of ethyl alcohol is pharmacodynamic. Nevertheless, alcohol so resembles food in its nutritive effects and is so commonly ingested as a dietary ingredient and as a beverage, that we must include it here. Whether it is in fact a food depends upon the definition. of food. Under the definition laid down by the Federal Food and Drugs Act, June 30, 1906, it is so classified. Aside from ethyl alcohol we must mention the higher alcohols which are more toxic the higher we ascend in the series. Fusel oil includes propyl, butyl, amyl and hexyl alcohols and is a common accompaniment of ethyl alcohol when the sugar used for fermentation is derived from starch. Amylic alcohol is an important constituent of the oil of mustard and horseradish.

TRIATOMIC ALCOHOLS.-Glycerin is a triatomic alcohol which, being joined to fatty acids, forms neutral fats such as stearin, olein, etc. Glycerin is a product in the digestion of fat and a by-product in the manufacture of soap. There is no satisfactory evidence of the value of glycerin as a foodstuff, but there is evidence to show that any excess of glycerin, which is consumed for therapeutic purposes, is not utilized in the system, but is decomposed into propionic and formic acids.

CYCLIC ALCOHOLS.-This classification includes the sterols. These, in general, belong to the terpene group, are solid at ordinary temperature

etc.

and yield terpenic acids on oxidation. They include cholesterol, isocholesterol, stercorin (koprosterin), phytosterol, cetyl alcohol, myricyl alcohol, Menthol may well be included in this group. In all probability some of the cholesterol of food is absorbed, but whether it is of service to the body is not clear. Since herbivora contain cholesterol, not phytosterol which they ingest, it seems that the body has the capacity of forming its own cholesterol, leaving it uncertain whether that absorbed from food furnishes any of the body supply.

Inositol, a hydroxy-derivative of hexahydrobenzene, is included with the cyclic alcohols as a matter of convenience and is mentioned because it is found in heart muscle.

ALDEHYDS.—Acetic aldehyd occurs in new spirits, especially when distillation is intermittent. Citrol, an acylic terpene of the formula. CH15.CHO, is of food interest because of its presence in the oil of citrous fruits, such as lemon, lime, orange, etc. Cyclic aldehyds are found in essential oils, as cinnamic aldehyd in oil of cinnamon. Furfurol and possibly other aldehyds of this type appear in pot-still spirits, being formed by the action of the fire (and possibly also by the acid) on the pentose of the woody fiber and gum contained in the husks, etc., suspended in the mash. They do not exist, except possibly in the minutest traces, in "patent spirits," which is a point of distinction. Benzaldehyd is formed from the glucosid amygdalin in bitter almonds, in cherry laurel and in fruit kernels. Vanillin, the active constituent of the vanilla bean, is methyl protocatechuic aldehyd.

ORGANIC ACIDS.-Organic acids arise by oxidation from both simple and complex compounds of carbon and hydrogen. Those derived from the alaphatic series, formula CnH2n+2, have the general formula CnH2nО ̧; those derived from the olefins, CnHn, have the general formula CnH2n-202. A list of the usual acids follows:

Organic acids are found as constituents of various foodstuffs. Some of these acids are formed by fermentation. Others are present in fruits, and in the process of ripening are progressively utilized in the formation of ethers, aldehyds and carbohydrates. Others are combined to form salts of potassium, sodium, calcium, and are mingled with their phosphates, sulphates and carbonates.

Formic Acid occurs in small proportions in honey. It is miscible with water and alcohol, possesses a pungent odor and piquant taste. It decom- poses carbonates and forms salts called formates.

Acetic Acid occurs in combination with alcohols in the esters of essential oils in many plants and is formed in the fermentation of many substances by the enzyme of mycoderma acetic, as in the manufacture of vinegar, which is discussed in the chapter on beverages and stimulants. It forms salts or acetates with sodium, potassium and other metals. The acetates occur normally in certain vegetable juices.

Butyric Acid is formed by the fermentation of lactic acid, a process known as butyric fermentation, and to some extent by the putrefaction of proteins. It exists as butyrin in butter to the extent of 6 per cent, but was not obtained in a recent investigation by distillation in vacuo, for which reason it has been suggested that its occurrence is due to decomposition of protein matter remaining in the butter. The acid possesses a pungent and disagreeable smell.

Glycollic Acid occurs in unripe fruits as the result of the oxidation of acetic acid and is in turn converted into glycollic aldehyd, which forms carbohydrates by polymerization.

Lactic Acid occurs in many plant juices. It is formed from sugar by what is known as lactic fermentation, which causes the presence of this acid in sour liquids and many sour fermented substances, as in sauerkraut, etc. It arises in consequence of the fermentation of lactose, as in the souring of milk in cheese-making, and ripening of cream; from the fermentation of various sugars, starch and other substances in the presence of nitrogenous animal matter. It is a thick, sour, hydroscopic, colorless, strongly acid liquid and mixes in all proportions with water and alcohol.

Oxalic Acid is widely distributed throughout the vegetable kingdom either as oxalic acid or oxalate. In the chapter on vegetable foods will be found a table giving the percentage of oxalic acids in a great many fruits and vegetables. It is formed from the oxidation of many substances such as glycerol, glucose, sucrose, alcohol and fats. It is also of considerable physiological interest in its origin and destination. When

ingested in food, it circulates into the animal tissues either as a free acid or salt. It undergoes oxidation to carbon dioxid and water. It is a question, however, whether the oxalic acid taken into the food is all excreted as carbon dioxid and water, or whether any of it is normally excreted unchanged.

Succinic Acid is a normal constituent in unripe fruits, especially in grapes, lettuce and other vegetables, and occurs in some animal secretions. It likewise is formed in the bacterial decomposition of carbohydrates and proteins, and as one of the metabolic products of yeast during alcoholic fermentation of sugar.

Malic Acid occurs in the juices of many fruits, as apples, currants, cherries, grapes, pineapples, blackberries, etc. It may be extracted from these fruits or it can be prepared synthetically. In combination with bases as malates, it occurs in sweet cherries, apples, rhubarb, gooseberries, grapes and strawberries.

Tartaric Acid occurs in the vegetable kingdom, especially in grapes, and some other fruits, largely as acid potassium tartrate. During the latter stages of the fermentation of grape-juice a considerable quantity of "argol" or crude cream of tartar is deposited, since it is no longer soluble in the alcohol-containing liquid.

Citric Acid occurs in the free state in many fruits, especially in lemons and tomatoes. It also occurs as citrates in lemons, limes, oranges, quinces, currants, gooseberries, strawberries, raspberries, cherries, cranberries, and other sour fruits. Citric acid is also constantly present in the milk of man and other mammals. Citric acid is absorbed from the alimentary canal and partly decomposed and excreted by the kidneys as sodium carbonate.

Benzoic Acid occurs as the free acid in cranberries and some other

fruits.

Salicylic Acid is reported to occur as a methyl-ester in currants, cherries, plums, grapes, crabapples, strawberries, blackberries, raspberries, mulberries, peaches, apricots, pineapples and oranges.

Gallic Acid is widely distributed in vegetables, especially in the form of compounds of tannins with glucosids. It occurs in tea leaves, nutgalls, claret, etc.

etc.

Tannic Acid occurs in gallnuts and in all kinds of bark, in coffee, tea, All tannins are amorphous and possess strongly astringent properties. Some are probably ester compounds of gallic acid with glucose. The acids of oils and fats will be described under their esters. ESTERS.-Chemically these are combinations of alcohol and acid and