as the fourteenth century, and have always been much prized for their flavor. They seem to grow best in the shade of nutbearing trees, and are propagated by spores like mushrooms. The truffle grows just beneath the surface of the soil to about the size of a potato and may be red, white or black. The most famous variety is the Périgord Truffle which is named from the French province, where it is found. In England dogs are trained to find the truffles, while on the Continent hogs are taught to discover them by the peculiar fleshy odor which they emit. They are used for garnishing dishes, and in flavoring soup and gravy, their value depending on their size, aroma and texture.

Preservation of Mushrooms

A common method of preserving mushrooms is by drying. They may be strung by means of a needle and thread, and dried in the sun, or over the stove, and when needed for use may be soaked in cold water. Large quantities of dried mushrooms are exported from Europe. Another method of preservation, especially in Russia, is by packing in salt and vinegar. In France the canning of mushrooms has grown to be an important industry, the young or unexpanded form, known as "buttons," being mostly employed. Before they are canned, mushrooms are often bleached by subjecting them to the fumes of sulfur dioxide. The imperfect fungi are also canned and sold for use in soups, etc., under the name "Champignons d'Hotel," which is understood to mean "buttons and pieces." "Mushroom catsup" is made by sprinkling the fungi with an abundance of common salt, and afterward boiling the juice with spices, and adding this to the chopped mushrooms, which have also been boiled.

Statistics

Most of the mushrooms imported into the United States come from France, with smaller quantities from Japan, Russia, and

Germany. The total quantity imported for the year ending Dec. 31, 1919, was 2,085,676 pounds, which is only one-third the quantity annually imported before the world war.

ALGÆ

Under the term algæ are included several varieties of seaweed, which are used as food. The most important of these is Irish moss or Carrageen, which is used both as ordinary food and in the dietary of invalids. It is abundant on rocky shores, especially those of Ireland, and grows from three-quarter tide to below low water mark. Several species of this seaweed are used. They are boiled for several hours until a slimy pulp is obtained, and this is sometimes made into cakes with oatmeal and fried in butter, or with vinegar and pepper is made into a sauce.

Composition

The chief constituent of Irish moss is a kind of mucilage which is known as "lichenin." The dried moss has been found by Church to contain 9.4 per cent. of nitrogenous matter and 55.4 per cent. of mucilage. As this mucilage is not affected by the saliva or pancreatic juice, and as the nitrogenous matter is not all of the digestible class, there is considerable question as to the nutritive value of this material.

Other edible algæ are the alaria or "murlins" of the north coasts, the dulse of the Scotch and Irish coast which forms a welcome addition to the potato diet of the peasants, and the agaragar or Chinese gelatin of the Orient. gelatin from sea weed by extracting it drying the gelatin obtained on cooling. with 300 parts of water, makes a firm jelly on cooling.

The Phillipinos make a with boiling water, and One part of this product

Edible Bird's Nests

The edible birds-nests, which find so much favor with the Chinese cooks are prepared from a semi-transparent substance made by

certain swallow-like birds that nest in high, rocky cliffs especially on the shores of Siam and the Malay Archipelago. The nests made by the birds from material obtained from alga which they gather, are robbed by the natives, but the birds patiently build again that they may rear their young.

LICHENS

The most important edible lichen is Iceland moss. It grows abundantly in the Arctic regions, and is sometimes made into bread or boiled with the milk of the reindeer. The bitter principle (acid) which the moss contains is partially removed by soaking in a weak solution of sodium carbonate. The jelly-like substance obtained by boiling the Iceland moss with water consists largely of lichenin or moss starch (C6H1005) and iso-lichenin. Although these substances are only slightly affected by the ordinary digestive juices, this moss must afford some nutriment, as it is an important food of the Laplanders and of their reindeer.

CHAPTER XII

ANIMAL AND VEGETABLE FATS AND OILS

Fats and oils may be divided into two general classes:

1. Essential or volatile oils.

2. Fixed oils and fats.

The essential oils are entirely different in their composition and properties from what are ordinarily known as fixed oils. They are volatile constituents of plants, and can usually be driven off unchanged by heat. As they are important constituents of Spices, a more complete discussion will be found under that head. (See P. 440.)

Fixed oils or fats are from two sources, viz: animals and vegetables.

Many of these substances are important constituents of foods, while others, differing only slightly in chemical composition, are utilized in various industries, as the making of soap, candles, paints, etc. Many of the animal oils, such as whale-oil, seal-oil, and fish-oil, are not agreeable to the taste of civilized people, but even these when properly treated and "hydrogenated" are used in increasing quantities as food. Most of the vegetable oils, if properly refined, make good food products. Vegetable oils are most frequently found in greatest abundance in the seeds. of plants, and are extracted by pressing the ground or crushed seed, or by extracting with some solvent like gasoline. Animal fats on the contrary are obtained from the animal tissues by a process of "rendering," or heating until the fat is melted, so that it can be separated from other animal matters.

Composition

Considered chemically, fats are glyceryl esters of fatty acids, or they may be looked upon as salts of the higher saturated or

unsaturated fatty acids in which the glyceryl acts as the base. Just as nitric acid when treated with caustic soda forms water and sodium nitrate (Chili salt peter), so stearic acid will theoretically combine with glyceryl to give glyceryl stearate (ordinary stearin). Some of the fatty acids contain a relatively higher proportion of hydrogen than others; those to which more hydrogen can be added we term unsaturated, while those that are fully supplied with hydrogen we speak of as saturated. To the former class belong oleic and linoleic acids, and to the latter stearic, palmitic, arachedic acid, etc.

Ordinary tallow is composed largely of stearic, palmitic and oleic acids combined with glycerol to form glycerides. The physical condition of the fat or oil, i.e., whether it is a solid or a liquid at ordinary temperatures, depends largely on the relative proportion of the saturated and unsaturated glycerides present.

Hardening of Oils

Recently a practical commercial method has been discovered1 for saturating the unsaturated glycerides by merely heating them with hydrogen in the presence of some catalytic agent such as nickel, so that now we have, instead of the liquid cotton-seed oil which is high in glyceryl oleate and low in the stearate, a white solid similar to tallow in which a considerable quantity of the oleate is changed to stearate. This process is also known as "hydrogenating." The change may be represented by the equation:

The work of Sabatier and Senderens has greatly advanced the processes used in the hardening of fats. The catalyzers used are of the two classes of metals, those of the nickel group, the only ones used commercially in the United States, and those of the platinum group. These when in a finely divided form are very 1 J. Soc. Ch. Ind., Vol. 31, p. 1115.