The hop plant is a twining, rough perennial having angular, rough, flexible stems, which twine around neighboring objects in a spiral direction from left to right, and climb to a great height. The leaves are opposite, and long petioled. The smaller are sometimes cordate; the larger have three or five lobes; all are serrate, of a deep green color on the upper surface, and, together with the petioles, extremely rough, with minute prickles. At the base of the petioles are two to four smooth, ovate, reflexed stipules. The flowers are numerous, axillary, and bracteate. The staminate flowers are a yellowish-white, and arranged in panicles; the pistillate, which grow on a separate plant, are pale green, and disposed in solitary, peduncled aments, composed of membranous scales, ovate, acute, and tubular at the base. Each scale bears, near its base, on its inner surface, two flowers, consisting of a roundish compressed ovary, and two styles, with long filiform stigmas. The aments are converted into ovate membranous cones or strobiles, the scales of which contain, each, at its base, two small achenes, surrounded by a yellow, granular powder-so-called lupulin. Only the pistillate plants are cultivated by the hop growers in Europe, and it is interesting to note that the unfertilized pistillate plants produce strobiles richer in aroma and more plenteous in lupulin. The plants flower in August and the fruits are harvested during September. The hops grown in this country contain a great many achenes, showing that the staminate plants are also cultivated. The strobiles are collected when the scales change from a light golden to a somewhat deeper hue.

The hop plant is a native of North America and Europe. In parts of New England, New York, Michigan and Indiana, it is extensively cultivated, and most of the hops consumed in the United States is supplied by those districts. Hops are also cultivated in Europe, Australia and South America. The part of the plant used is the fruit or strobiles. These, when fully ripe, are picked, dried by artificial heat, packed in bales or hemp bags, and sent into the market.

By separating the volatile oils and determining its acid and ester value, Rabak (C. D., Ixxxv, 376) is able to distinguish American grown from imported hops. He finds that the European hops always show a lower ester value in the volatile oil than do the American. Hops consist of numerous thin, translucent, veined, leaf-like scales, which are of a pale greenish-yellow color, and contain near the base two small, round, black achenes.

Powdered Hop. � Light yellowish green; numerous fragments of wavy-walled lignified epidermal tissue; fragments of parenchyma tissue with many of the cells containing calcium oxalate in rosettes and associated with branching tracheae, the latter haying spiral markings; numerous unicellular, slightly curved non-lignified hairs with walls frequently silicified, occurring either isolated or attached to fragments of epidermal tissue; numerous rosettes of calcium oxalate up to 0.024 mm. in diameter; glandular hairs with multi-cellular heads filled with yellowish oil from 0.100 to 0.300 mm. in diameter or frequently broken (lupulin); few glandular hairs with nearly colorless multi-cellular heads; few spherical, spinose yellowish pollen grains up to about 0.024 mm. in diameter; a few lignified fibers; few fragments of parenchyma tissue with large cells containing eystoliths of calcium carbonate. " Preserve Hop in tightly closed containers, protected from light." N.F.

Though brittle when quite dry, they are pulverized with great difficulty. Their odor is strong, peculiar and fragrant; their taste very bitter, aromatic, and slightly astringent. Their aroma, bitterness, and astringency are imparted to water by decoction, but the first mentioned property is dissipated by long boiling. The most active part of hops is the lupulin (see Lupulinum). Hops are often subjected in Germany to the fumes of burning sulphur, because of the supposition that they keep better when thus treated. Besides, by being partially bleached by the process, old hops, which have suffered from time, having become darker, generally spotted, and weaker, assume a brighter appearance, as if fresher, and generally command a better price in the market. To detect the consequent presence of sulphurous acid, the brewers put a silver spoon in a mixture of hops and water, under the impression that it will produce a black stain upon the silver. But this test will answer only when applied within a fortnight after the use of the sulphur. A more delicate method is that of Heidenreich, who puts twenty or thirty strobiles of the hops in a flask with zinc and hydrochloric acid, and passes the hydrogen evolved through solution of lead acetate. If sulphurous acid be present, hydrogen sulphide will be produced, which will occasion a dark precipitate with the solution. But even this plan often fails when the hops have been kept more than three or four weeks. A modification of this test has been proposed by R. Wagner. For the solution of lead acetate used in Heidenreich's method there is to be substituted a solution of sodium nitroprusside, so weak as to have a very light brown color, to which have been added a few drops of solution of potassium hydroxide. If the gas evolved contain the minutest proportion of sulphur, a violet color will be produced when the first bubble passes into the solution; and this will, by a continuance of the process become a magnificent purple. The least trace of sulphurous acid may thus be found, but a few months after the sulphuring of hops none at all can be detected.

Hops are said to be sometimes threshed in order to separate the lupulin, which is sold separately. Their efficiency is thus, no doubt, greatly impaired. Hops thus treated have the scales more or less broken; and any parcel presenting this appearance is to be suspected. Hops often contain a variable quantity of lupulin in consequence of the granules of this substance separating, especially on agitation, and seeking the lower portion of the mass, which thus becomes richer, while the upper is poorer. They should always be examined in reference to the lupulin they contain, and, if nearly or quite destitute of it, should be deemed of inferior value and not be used medicinally.

Constituents. � Hops contain two crystallizable bitter substances of an acid character, and three resins, two of which are soft in character and bitter in taste and are present to the extent of over 10 per cent., and one of which is hard in character and tasteless and present to the extent of less than 5 per cent. The two soft resins probably contribute the most valuable properties of the hops, although the insoluble bitter acids, according to some authorities, are hydrolized in preparing the wort and become bitter and communicate foaming properties to the liquid by changing the surface tension. The investigation of the acids showed the alpha acid to have the composition C₂₁H₃₀O₄ and to contain a carboxyl group and a ketonic group. It is probable that this acid exists in the hops, condensed with a valeric acid residue. There is also present humulone, C₂₈H₃₂O₅, a lactone which is probably a product of the hydrolysis of the alpha acid. It is also probable that the alpha resin is a simple polymer of the alpha acid. The beta acid, C₂₅H₃₆O₄, is also called lupulinic acid and yields valeric acid on oxidation. The essential oil of hops contains myrcene.

Lupulite, a name formerly applied to the bitter substance of hops, is not a chemical individual. W. Wollmer states that the bitter principles of hops, C₂₁H₃₀O₄ and C₂₆H₃₀O₅, are not true acids, but owe their acid character to their hydroxyl groups. He therefore prefers to call them humulone and lupulone. He split humulone into carbon dioxide, isopentane, and a body, C₁₆H₂₄O₅; while lupulone was broken into isopentane and a body, C₂₁H₃₄O₄. Both humulone and lupulone on boiling with alkali yield humulinic acid, C₁₅H₂₂O₄, and an unsaturated acid, C₆H₁₀O₂. (Chem. Abstracts, 1919, xiii, 495.) There is present also a peculiar tannin known as humulo-tannic acid, which is hydrolizable into glucose and a substance called hop-red. (See also Lupulinum.)

References to the literature of hops will be found in Tr. Chem. Soc., 1913, ciii, p. 1267, Power and Tutin; in Proc. Chem. Soc., 1913, xxix, p. 132, Chapman; in Jour, of the Industry of Brewing, 1913, xix, p. 261, Garrigues; in Rep. Pharm., 1922, xxxii, p. 322, and in J. Soc. Chem. Ind., 1920, xxxix, p. 498a.

Uses. � Hops is an aromatic bitter and hence may be useful in atonic dyspepsia. By many they are believed to have a sedative effect on the nervous system and are used in hysteria, restlessness, insomnia, and the like. Whether this latter action is due to anything more than an effect through the imagination is open to question.

An infusion prepared with half an ounce of hops and a pint of boiling water may be given in the dose of four fluidounces (120 cc.). The tincture was a British official preparation of hops, but the alcohol probably acts more decidedly upon the system than the hops. The fluidextract of hops of the N. F. is superior because of the relatively smaller amount of alcohol. A pillow of hops has proved useful in allaying restlessness and producing sleep in nervous disorders. They should be moistened with water, containing a trace of glycerin, previously to being placed under the head of the patient, in order to prevent rustling. Fomentations with hops, and cataplasms made by mixing them with some emollient substance, are often beneficial in local pains and tumefactions.