CONTAGION, in physic, the commu nicating a disease from one body to ano ther. In some diseases it is only effected by an immediate contact, as in the syphi lis ; in others it is conveyed by infected clothes ; and in others it seems capable of being transmitted through the air at a considerable distance. Though a very able writer in Dr. Rees's Cyclopedia produces a variety of facts, to prove that the most malignant contagions are never conveyed to any great distance through the atmosphere, but that they are in fact rendered inert and harmless by diffusion in the open air, and even in the air of a well ventilated apartment. Hence the same writer, who has arti cle of great interest on this Subject, in fers that all pestilence is propagated by near approach to, or actual contact of, the disease, or by the conveyance of the contagious poison in articles impregnat ed with it. This noxious. matter as rut many cases readily distinguished by the peculiarly disagreeable smell which it communicates to the air. No doubt this Matter differs according to the diseases which it communicates, and the sub stance from which it hasoriginated. Mor veau lately attempted to ascertain its nature ; but he soon found the chemical tests hitherto discovered altogether in sufficient for that purpose." He has put it beyond a doubt, however, that the noxi ous matter which rises from putrid bo dies is of a compound nature ; and that it is destroyed altogether by certain agelits, particularly - by those, gaseous bodies which readily with their oxygen. He exposed air infected by putrid bodies to the action of various substances ; and he judged of the result by ,the effect' which these bodieS had in destroying the, fetid smell of the air. The' following is the result of his • experiments :'odorous bodies, such, as benzoin, aromatic, plants, &c. have no whatever : neither have the solutions of myrrh, benzOin, &c. in alcolil, though agitated in infected air. Pyrolignous acid is equallyinert. Gun-. powder, when fired in infected air, dis places a portion of it ; but what. remains still retains its fetid odour. Sulphuric
acid has no effect; sulphurous acid ens the odour, but does not destroy it. Vinegar diminishes the odour, but its ac tion is slow and incomplete. Acetic acid acts instantly, , and 'destroys the_ fetid odour of infected air completely. The fumes of nitric acid, first employed by Dr. Carmichael Smith, are equally effica cious. Muriatic acid gas first pointed out as a proper agent by Molweau himself, is equally ineffectual. But the most pow erful agent is oxymuriatic acid gas, first proposed by Mr. Cruickshanks, and now employed with the greatest success in the British navy and military hospitals.
We shall observe, that these gases are readily procured. Nitre, or, as it is , call ed in the new chemistry, nitrate of pot ash, mixed with sulphuric acid, yields a very powerful gas, the acid combining with the potash, the base of the nitre, expels the nitrous gas in fumes. Muriatic acid gas is - obtained in a similar manner by using common salt, the alkali combines with the acid, and the muriatic gas goes off in vapour. Prevention be ing, however, much better than the means of cure, we shall give some rules for the management of persons sick with contagious diseases. Cleanliness is es sentially necessary : the chamber door should ever be kept open, and the win dows as much as possible in the day ; the bed curtains should notbe drawn, except to ward off the direct light from the window : dirty clothes, utensils, &c. should be frequently changed, and wash ed very clean : all discharges from the patient should be instantly removed : visitors and attendants should avoid the patient's breath, and the vapour from his body, and from all evacuations ; they should never go into an infected chamber with an empty stomach, and on coming from it they should blow their poses and expectorate freely.
During the prevalence of a contagious epidemic, great care should be taken to avoid all causes of debility, and to pre serve an equal state of The gene ral alarm which prevails on such occa sions contributes, not, a little, to extend the evil.