Diorama. See PANORAMA. Diorite. See IGNEOUS ROCKS, PETROGRAPHY. Dioscorea'ceæ, an order of Monocotyledons, of which the genus Dioscorea (see YAM) is the type. There are about 170 species, temperate or tropical, all twining shrubs, with large rootstocks or tubers. Testudinaria elephantipes, a South African species, sometimes called Elephant's Foot and Hottentots' Bread, has a large fleshy rhizome, with a rough cracked bark, which is used as food by the Hottentots in times of scarcity. Tamus communis (Black Bryony) is the only British representative of the order.

Diosco'ridés, PEDACIUS, or PEDANIUS, a Greek physician, was a native of Anazarba in Cilicia, and, probably in the 2d century of our era, accompanied the Roman armies as physician through many countries. He has left a great work on materia medica, in five books, in which he treats of all the then known medicinal substances and their properties, real or reputed. His authority in botany and materia medica was long undisputed, and is still maintained in the East. The best editions of Dioscorides, including some smaller works bearing his name, are by Saracenus (1598) and Sprengel (2 vols. 1829-30).

Dioscuri. See CASTOR AND POLLUX.
Diosma. See BUCKU.

Diospyros. See DATE PLUM, and EBONY.

Dip, in Geology, is the inclination of strata downwards into the earth. The amount or angle of dip is the degree of deviation from a level line, or the plane of the horizon. See HORIZON.

so

Diphtheria (Gr. diphthera, 'a pellicle') was described in 1826 by M. Bretonneau of Tours as a form of very fatal sore throat, occurring chiefly in children. In its milder forms the disease resembles other inflammations in the throat, but a case can be recognised by the finding of the diphtheria bacillus in the inflamed area. The disease begins by malaise, feeling of chilliness, loss of appetite, headache, and more or less fever; soon the throat feels hot and painful, whilst Je neck is stiff and tender. If seen early, the threat is red and swollen, but a false membrane of yellowish or grayish colour quickly appears in spreading patches on an inflamed and ulcerated base in the pharynx or back of the throat, and often extends down the phagus or gullet, one side usually being more affected than the other. There may be enlargement of the glands at the angle of the jaw, and albuminuria generally occurs at some stage of the disease. Diphtheritic membrane may be got on any mucous surface, or even on a wound; if it extends into the larynx, it gives rise to difficulty in breathing. The throat affection is often accompanied by a low and very dangerous form of fever, with great and rapid loss of the patient's strength, which is still further reduced by difficulty in taking food; in other cases, the disease is fatal by paralysis of the heart, or by suffocation, due to invasion of the larynx, when tracheotomy may require to be resorted to. After the acute disease is over, the recovery may be delayed by paralytic symptoms of various kinds; or simply by extreme debility, with exhaustion and loss of appetite. Diphtheria is contagious, the bacillus being conveyed from individual to individual by the air, and it has the peculiar tendency of tacking itself on to other diseases, especially scarlet fever. Damp and temperate climates seem to favour its development, while the contagium may remain dormant for long

periods. Outbreaks are stated to have been traced to impure drainage and bad water. One attack affords only slight protection against recurrence. Diphtheria is caused by the diphtheria bacillus, discovered by Loeffler in 1884. The organism, multiplying in the throat, gives rise to the local inflammation, and also produces a powerful poison which, being absorbed into the body, causes the heart weakness and the paralysis alluded to above. This latter fact was proved by Roux of Paris find ing that when the bacilli are grown in beef broth and subsequently removed by filtration through an earthenware filter, the remaining fluid or toxin, on injection into animals, gives rise to typical post-diphtheritic paralysis. The discovery led to Behring in 1893 elaborating the idea of treating the disease by antitoxin. If such an animal as the horse receives every few days increasing doses of the toxin, its serum, after two or three months, is found to contain a substance-antitoxin-which, when injected into animals, protects them against infection either with the diphtheria bacillus or its toxin; furthermore, even after infection, injections of the antitoxin will in a great many cases prevent death. Behring found that the last fact was also true in natural infection occurring in man, the inflammation in the throat being checked, and the general toxic effects being minimised. The antitoxin treatment thus discovered has diminished the mortality of diphtheria from 45 per cent. to about 10 per cent. Its success depends on its early application, if possible on the first day of the disease. A method was devised by Schick in 1913 of discovering by inoculation persons susceptible to diphtheria. The administration of a small dose of antitoxin to these affords protection against the disease. Besides the administration of antitoxin, the treatment consists in keeping up the strength of the patient by means of concen trated beef-tea, milk, egg-flip, &c. Iron in large doses is most valuable, and sometimes quinine. Locally, solvents, such as lactic acid, are applied to the throat by a brush; antiseptics are also useful, the best being Condy's fluid. It has been found that after an attack of diphtheria the bacilli may remain in the throat for weeks or months. It is chiefly by means of such diphtheria carriers' that the disease is kept alive in a community and fresh outbreaks originated. A diphtheria convalescent should not be allowed to mix with healthy people till bacteriological investigation has shown that no living diphtheria bacilli remain in

the throat.

Diphthong. See PHONETICS, SPELLING.

Diplod'ocus, a gigantic dinosaur of the suborder Sauropoda, found in the Jurassic rocks of the western states of the American Union. One of the largest (if not the very largest) of animals known to have walked this globe, it had a comparatively short and low body, a small head, with slender teeth only in the front parts of the jaws, a very long neck, and was herbivorous and apparently aquatic. The total length was perhaps 75 or 80 feet, of which 20 fell to the neck and only 2 to the head; the weight must have been some 20 tons. In 1905 Mr Carnegie presented a cast of one from the mountains of Wyoming to the British Museum. The name was coined in 1878 by Dr O. C. Marsh (q.v.), to whom we owe the knowledge of so many of these dinosaurs, and is derived from Gr. diploos, double,' and dokos, 'beam' or 'bar.' See DINOSAURIA.

Diplo'ma (Gr., 'something doubled'), originally a document on two tablets of wax (see DIPTYCH), or on writing material which was folded. The Roman emperors granted diplomas to couriers, giving them the use of public servants and horses;

hence diploma came to signify an official warrant of any kind. The term is now mostly applied to documents given by universities and other learned societies, in proof of the holder having attained a certain degree; to the licenses held by physicians and surgeons; and to certificates of merit awarded at exhibitions.

Diplomacy (from diploma in the sense of public document'), the art of conducting the intercourse and adjusting the mutual relations of nations, arises out of the necessary interdependence of states, and the rights and duties of political intercourse. Although the art (of diplomacy is as old as official intercourse between states, the special class of officials now known as diplomatists did not, and could not, exist until permanent legations were instituted. The general rules regulating the authority of accredited diplomatic representatives and the means by which the intercourse between states is conducted, are embodied partly in international usages and partly in treaties.

The classification of diplomatic agents resident in foreign countries was regulated by the protocols of the Congress of Vienna in 1815, and the Congress of Aix-la-Chapelle in 1818. It is as follows: (1) Ambassadors and papal legates or nuncios; (2) envoys extraordinary, or ministers plenipotentiary; (3) ministers resident accredited to the sovereign; (4) chargés d'affaires accredited, not to the sovereign, but to the minister for foreign affairs. This classification is only of importance in relation to questions of precedence and ceremonial. In the diplomatic hierarchy ambassadors, being considered personal representatives of the heads of their states, enjoy special honours. Thus in the United Kingdom they rank in precedency immediately after the princes of the blood-royal.

A diplomatic agent is furnished with a letter of credence, announcing his appointment and requesting that full faith and credit be given to what he shall say on behalf of his state. This letter is presented by him to the government to which he is sent. Where a diplomatic envoy is entrusted with the conduct of specific negotiations, which are outwith the ordinary business of a permanent legation, e. g. the negotiation of a commercial treaty, it is necessary to furnish him with special powers, which may either be contained in the letter of credence, or, as is more usual, may be conferred by letters patent.

The most complete personal independence and freedom of action are essential to the efficient performance of the duties of a diplomatic agent. The inviolability of international agents was recognised by the nations of antiquity, and has been right of legation. This privilege is enjoyed from accepted in modern times as inseparable from the the moment that a diplomatic envoy enters the territory of the state to which he is accredited until he leaves that territory. During his residence in that state he continues to be domiciled in, and to be entitled to the protection of the municipal laws of his home state. He is exempt from the jurisdiction, both civil and criminal, of the state in which he resides. Thus, in England a

foreign ambassador cannot be sued against his will, even in respect of private commercial transactions; and this privilege extends to his family and suite, attachés and secretaries, and domestic servants. This immunity, which is absolute in the case of an ambassador himself, is forfeited in the case of a member of his establishment if such a person engages in trade. The official residence of an ambassador cannot be entered by officers of justice, police, or revenue of the state to which he is accredited, unless he specially permits such entry. His residence is, indeed, by a fiction of law, held