Page:Encyclopædia Britannica, Ninth Edition, v. 7.djvu/276

258 DISCUS, a quoit, or circular plate of stone or metal, 10 or 12 inches in diameter, which was used by the ancient Greeks and Romans for throwing to a distance as a gymnastic exercise. Sometimes a kind of quoit of a spherical form was used for the same purpose; and through a hole in its centre a thong was passed, to assist the player in throwing it. Statius, in Theb., vi. 646–721, fully explains the manner in which the discus was used. In the British Museum there is a copy of a famous statue by Myron of a discobolus in the act of throwing the discus.  DISINFECTANTS are agents or substances employed to prevent the spread of contagious or infectious disease. Recent investigations all tend to demonstrate that the efficiency of any disinfectant is due to its power of destroying, or of rendering inert, specific poisons or disease germs which possess in themselves an independent existence; and which, when introduced into the animal system, under favourable conditions, increase and multiply, thus pro ducing the phenomena of special diseases. Therefore, antiseptic substances generally, which check or stop putrefactive decay in organic compounds, by preventing the growth of those minute organisms which produce putrefaction, are, on that account, disinfectants. So also the deodorizers, which act by oxidizing or otherwise changing the chemical constitution of volatile substances disseminated in the air, or which prevent noxious exhala tions from organic substances, are in virtue of these properties effective disinfectants in certain diseases. A knowledge of the value of disinfectants, and the use of some of the most valuable agents, can be traced to very remote times; and much of the Levitical law of cleansing, as well as the origin of numerous heathen ceremonial practices, are clearly based on a perception of the valua of disinfection. The means of disinfection, and the substances employed, are very numerous, as are the classes and condi tions of disease and contagion they are designed to meet. Nature, in the oxidizing influence of freely circulating atmospheric air, in the purifying effect of water, and in the powerful deodorizing properties of common earth, has pro vided the most potent ever-present and acting disinfecting media. Of the artificial disinfectants employed or available three classes may be recognized:—1st, volatile or vaporizable substances, which attack impurities in the air; 2d, chemical agents for acting on the diseased body or on the infectious discharges therefrom; and 3d, the physical agencies of heat and cold. In some of these cases the destruction of the contagium is effected by the formation of new chemical compounds by oxidation, deoxidation, or other reaction, and in others the conditions favourable to life are removed or life is destroyed by high temperature. Of the first class—aerial disinfectants—those most employed are the gaseous sulphurous anhydride, the fumes of nitrous acid and other acid substances, including vaporized carbolic acid, with chlorine gas and the vapours of bromine and iodine. The use of sulphurous anhydride, obtained by burning sul phur, is of great antiquity, and it still is unequalled as a disinfectant of air on account both of its convenience and general efficacy. Camphor and some volatile oils have also been employed as air disinfectants, but their virtues lie chiefly in masking, not destroying, noxious effluvia. In the 2d class—non-gaseous disinfecting compounds—all the numerous antiseptic substances may be reckoned; but the substances principally employed in practice are oxidizing agents, as potassic manganates and permanganates (Condy's fluid), and solutions of the so-called chlorides of lime, soda, and potash, with the chlorides of aluminium and zinc, soluble sulphates and sulphites, solutions of sulphurous acid, and the tar products—carbolic, cresylic, and salicylic acids. DrJ. Dougall of Glasgow found the following sub stances the most powerful in destroying minute forms of life:—Sulphate of copper, chloride of aluminium, chromic acid and bichromate of potassium, bichloride of mercury, benzoic acid, bromal hydrate, chloral hydrate, hydrocyanic acid, alum, hydrochlorate of strychnia, ferrous sulphate, arsenious acid, and picric acid. Of the physical agents heat and cold, the latter, though a powerful natural disin fectant, is not practically available by artificial means; heat is a power chiefly relied on for purifying and disinfect ing clothes, bedding, and textile substances generally. Different degrees of temperature are required for the destruction of the virus of various diseases; but as clothing, &c., can be exposed to a heat of about 250°. without injury, provision is made for submitting articles to nearly that temperature. For the thorough disinfection of a sick room the employment of all three classes of disinfectants, for purifying the air, for destroying the virus at its point of origin, and for cleansing clothing, &c., may be required.  DISLOCATION. This term is applied in surgery to the displacement from each other of the cartilaginous or articular surfaces of the bones entering into the formation of a joint. In a normal joint these surfaces are in contact and held together by ligaments and muscles; in a dislocated joint they are separated more or less completely—in the great majority of cases by external violence; in some instances, however, by powerful muscular exertion. The ease with which a joint is dislocated varies with the form and structure of the joint and with the position in which tho joint is when the force is applied. The relative frequency of fracture and dislocation depends on the strength of the bones above and below tho joint relatively to the strength of the joint. These points may be illustrated by examples from the joints of the arm and leg, because, with perhaps the exception of the joint between the lower jaw and tho skull, it is in these situations that dislocation is most fre quently observed. The strength of the different joints in the body is dependent on either ligament, muscle, or the shape of the bones. In the hip, for instance, all three sources of strength are present; therefore, considering tho great leverage of the long thigh bone, the hip is rarely dislocated. The shoulder, in order to allow of extensive movement, has no osseous or ligamentous strength; its strength is muscular, therefore it is frequently dislocated, because the muscular strength varies in power, the muscles may be relaxed, the person is unprepared, and dislocation occurs; if, on the other hand, the muscles are tense, and the patient is prepared for the strain, then the result will be either a sprain of the joint or a fracture of one of the adjoining bones. The wrist and ankle are rarely dislocated; in the wrist the radius gives way, in the ankle the fibula, these bones being relatively weaker than the respective joints. The wrist owes its strength to ligament, the ankle to the shape of the bones. The elbow is osseously strong, but this strength necessarily varies with the position of the arm. The symptoms of a dislocation are distortion and limited movement, with absence of the grating sensation felt in fracture when the extremities of a broken bone are rubbed together. The treatment consists in reducing the dislocation. The sooner this is done the better—the longer the delay the more difficult it becomes to remedy the displacement. After a variable period, depending on the nature of the joint and the age of the person, it may be impossible to replace the bones. The result will be a more or less useless joint. The administration of chloroform, by relaxing the muscles, greatly assists the operation of reduction. The length of time that a joint has to be kept quiet after it has been restored to its normal shape depends on its form; if osseously strong, then early movement is allowable, as in the elbow joint; if osseously weak, then early movement is unjustifiable. More especially is this the case when, associated with osseous 