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 Dragonflies (London, 1899). For wings and mechanism of flight, R. von Lendenfeld, ''S.B. Akad. Wien'', lxxxiii. (1881), and J. G. Needham, ''Proc. U.S. Nat. Mus.'' xxvi. (1903). For general morphology, R. Heymons, ''Abhandl. k. preuss. Akad. (1896), and Ann. Hofmus. Wein'', xix. (1904).

 DRAGON’S BLOOD, a red-coloured resin obtained from several species of plants. Calamus draco (Willd.), one of the rotang or rattan palms, which produces much of the dragon’s blood of commerce, is a native of Further India and the Eastern Archipelago. The fruit is round, pointed, scaly, and the size of a large cherry, and when ripe is coated with the resinous exudation known as dragon’s blood. The finest dragon’s blood, called jernang or djernang in the East Indies, is obtained by beating or shaking the gathered fruits, sifting out impurities, and melting by exposure to the heat of the sun or by placing in boiling water; the resin thus purified is then usually moulded into sticks or quills, and after being wrapped in reeds or palm-leaves, is ready for market. An impurer and inferior kind, sold in lumps of considerable size, is extracted from the fruits by boiling. Dragon’s blood is dark red-brown, nearly opaque and brittle, contains small shell-like flakes, and gives when ground a fine red powder; it is soluble in alcohol, ether, and fixed and volatile oils. If heated it gives off benzoic acid. In Europe it was once valued as a medicine on account of its astringent properties, and is now used for colouring varnishes and lacquers; in China, where it is mostly consumed, it is employed to give a red facing to writing paper. The drop dragon’s blood of commerce, called cinnabar by Pliny (N.H. xxxiii. 39), and sangre de dragon by Barbosa was formerly and is still one of the products of Socotra, and is obtained from Dracaena cinnabari. The dragon’s blood of the Canary Islands is a resin procured from the surface of the leaves and from cracks in the trunk of Dracaena draco. The hardened juice of a euphorbiaceous tree, Croton draco, a resin resembling kino, is the sangre del drago or dragon’s blood of the Mexicans, used by them as a vulnerary and astringent.

 DRAGOON (Fr. dragon, Ger. Dragoner), originally a mounted soldier trained to fight on foot only (see ). This mounted infantryman of the late 16th and 17th centuries, like his comrades of the infantry who were styled “pike” and “shot,” took his name from his weapon, a species of carbine or short musket called the “dragon.” Dragoons were organized not in squadrons but in companies, like the foot, and their officers and non-commissioned officers bore infantry titles. The invariable tendency of the old-fashioned dragoon, who was always at a disadvantage when engaged against true cavalry, was to improve his horsemanship and armament to the cavalry standard. Thus “dragoon” came to mean medium cavalry, and this significance the word has retained since the early wars of Frederick the Great, save for a few local and temporary returns to the original meaning. The phrases “to dragoon” and “dragonnade” bear witness to the mounted infantry period, this arm being the most efficient and economical form of cavalry for police work and guerrilla warfare. The “Dragonnades,” properly so called, were the operations of the troops (chiefly mounted) engaged in enforcing Louis XIV.’s decrees against Protestants after the revocation of the edict of Nantes. In the British service the dragoons (1st Royals, 2nd Scots Greys, 6th Inniskillings) are heavy cavalry, the Dragoon Guards (seven regiments) are medium, as are the dragoons of other countries. The light cavalry of the British army in the 18th and early 19th century was for the most part called light dragoons.

 DRAGUIGNAN, the chief town of the department of the Var in S.E. France; 51 m. N.E. of Toulon, and 28 m. N.W. of Fréjus by rail; situated at a height of 679 ft. above the level of the sea, at the southern foot of the wooded heights of Malmont, and on the left bank of the Nartuby river; pop. (1906) 7766. It possesses no notable buildings, save a modern parish church, a prefecture, also modern, and a building wherein are housed the town library and a picture gallery, with some fair works of art. In modern times the ramparts have been demolished, and new wide streets pierced through the town.

 DRAINAGE OF LAND. The verb “to drain,” with its substantives “drain” and “drainage,” represents the O. Eng. dreahnian, from the same root found in “dry,” and signifies generally the act of drawing off moisture or liquid from somewhere, and so drinking dry, and (figuratively) exhausting; the substantive “drain” being thus used not only in the direct sense of a channel for carrying off liquid, but also figuratively for a very small amount such as would be left as dregs. The term “drainage” is applied generally to all operations involving the drawing off of water or other liquid, but more particularly to those connected with the treatment of the soil in agriculture, or with the removal of water and refuse from streets and houses. For the last, see ; the following article being devoted to the agricultural aspects of this subject. See also the articles, , , , and (law).

Agricultural or field drainage consists in the freeing of the soil from stagnant and superfluous water by means of surface or underground channels. It may be distinguished from the draining of land on a large scale which is exemplified in the reclamation of the English Fens (see ). Surface drainage is usually effected by ploughing the land into convex ridges off which the water runs into intervening furrows and is conveyed into ditches. For several reasons this method is ineffective, and, where possible, is now superseded by underground drainage by means of pipe-tiles. Land is not in a satisfactory condition with respect to drainage unless the rain that falls upon it can sink down to the minimum depth required for the healthy development of the roots of crops and thence find vent either through a naturally porous subsoil or by artificial channels.

A few of the evils inseparable from the presence of overmuch water in the soil may be enumerated. Wet land, if in grass, produces only the coarser grasses, and many subaquatic plants and mosses, which are of little or no value for pasturage; its herbage is late in spring, and fails early in autumn; the animals grazed upon it are unduly liable to disease, and sheep, especially, to foot-rot and liver-rot. In the case of arable land the crops are poor and moisture-loving weeds flourish. Tillage operations on such land are easily interrupted by rain, and the period always much limited in which they can be prosecuted at all; the compactness and toughness of the soil renders each operation more arduous, and its repetition more necessary than in the case of dry land. The surface must necessarily be thrown into ridges, and the furrows and cross-cuts cleared out after each process of tillage, and upon this surface-drainage as much labour is expended in twenty years as would suffice to make under-drains enough to lay it permanently dry. With all these precautions the best seed time is often missed, and this usually proves the prelude to a scanty crop, or to a late and disastrous harvest. The cultivation of the turnip and other root crops, which require the soil to be wrought to a deep and free tilth, either becomes altogether impracticable and must be abandoned for the safe but costly bare fallow, or is carried out with great labour and hazard; and the crop, when grown, can neither be removed from the ground, nor consumed upon it by sheep without damage by “poaching.”

The roots of plants require both air and warmth. A deep stratum through which water can percolate, but in which it can never stagnate, is therefore necessary. A waterlogged soil is impenetrable by air, and owing to the continuous process of evaporation and radiation, its temperature is much below that of drained soil. The surface of the water in the supersaturated soil is known as the “water-table” and is exemplified in water standing in a well. Water will rise in clay by capillarity to a height of 50 in., in sand to 22 in. Above the “water-table” the water is held by capillarity, and the percentage of water held decreases as we approach the surface where there may be perfect dryness. Draining reduces the “surface tension” of the capillary water by removal of the excess, but the “water-table” may be many feet below. Drains ordinarily remove only excess of capillary water, an excess of percolating water in wet weather.

In setting about the draining of a field, or farm, or estate, the first point is to secure a proper outfall. The lines of the receiving drains must next be determined, and then the direction of the