(3) The natural means of purifying the atmosphere are diffusion, oxidation, the action of winds, and the fall of rain. In cases where the air is specially impure, as in sick-rooms where there are contagious cases, the agents commonly known as d4s-infeet ants (q.v.), or deodorants, are employed. Amongst the welds of this class are charcoal (see WOOD-CHARCOAL), dried earth, and the carbolates of lime and magnesia. Amongst the liquids, those in highest reputation are Candy's fluid+ (consisting of an alkaline per manganate, which at once decomposes ammoniecal compounds, and destroys organic matter rapidly) and carbolic acid: whilst amongst the rases or vapors—which me the Most powerful means of purifying the atmosphere, next to ventilation—may be espe cially mentioned chlorine, nitrous acid, and sulphurous acid; of these, says Dr. Parkes, the, nitrous acid is probably ti-e most powerful, but it is useful to employ all three alternately, or even together. It must be recollected that all these agents are mere auxiliaries to ventilation, the primary importance of which must never he forgotten.
(4) Abundant experience confirms the view which might have been a pri‘eri inferred from the study of the physiology of respiration (q.v.), that the breathing of impure air must be incompatible with perfect health. The special humilities are worthy of notice as being causes of disease, or of an impaired state of health, are arranged by Dr. Parkes as follows: (a) Suspended matters; (b) Gaseous matters; (c) Impurities from sev eral substances always co-existing.
(a) The suspended matters which are known to occasion disease in various trades are Very numerous. Thackrah, in his well-known work on The Effects of Arts. Trades, and on health, published in 1832. gives the following list of workmen who were injuriously affected by the dust of their trades; Corn-millers. maltsters, tea-men, coffee roasters, snuffmakers, paper-makers. flock-dressers, feather-dressers, shoddy-grinders, weavers of coverlets, weavers of !larding, dressers of hair, halters employed in the bow ing department, dressers of colored leather, workers in flax, dressers of hemp, some workers in wood, ware-grinders, masons, colliers, iron-miners, lead-miners. grinders of metals, 111e-cutters, machine-makers, makers of fire-arms, and button-makers. To this list must be added colliers, who suffer from lung-disease in ill-ventilated mines; potters, especially the class called flatTressers, in whem emphysema is so common that it is known as "the potters' astlima;" the china-scourers, who all, sooner or later, become astlimatical from inhaling the light flint-dust in suspension; pearl button-makers and pin-pOinters, who suffer from bronchitis and haemoptysis; the makers of grinding stones; the makers of Portland cement, etc. In some trades irritant vapors are more or
less assorilted with suspended particles in causing disease. Brass-founders suffer not only bronchitis and asthma from the inhaled dust, but also a special disease, described by Dr. Greenhow (in the Proceedings of the Medico- Chirurg. Soc. vol. 4) as brass-founders' ague. which is apparently produced by the inhalation of the fumes of oxide of zinc; the symptoms being oppression of the chest, with indefinite nervous sensations, followed by shivering, a hot stage, .and profuse sweating. Coppersmiths and tin-plate are liable to somewhat similar attacks. Plumbers, house-painters, manufacturers of white-lead, etc., are, as is well known, liable to lend poisoning. The peculiar affection tb which workers in mercury and its amalgams, as silverers and water-gilders, are exposed, is described in the article PARALYSIS, under the name of mercurial tremor, or the tremt;les. In the various trades iu which arsenical compounds are employed, as in making artificial flowers, green paper for walls, etc., preparing arsenical pigments, etc., the well-known symptoms of chronic arsenical poisoning are likely to ensue. On the subject, Dr. Guy has, at the request of government, drawn up an elaborate report.
Passing from inorganic or unorganized matter to organic substances floating in the atmosphere, and giving rise to a large class of important diseases, we may remark that it still remains to be decided in what exact condition this organic matter exists—whether it is in the form of impalpable particles, or moist or dry epithelial or puss cells; " and whether it is always contained iu the substances discharged or thrown off horn the body (as is certainly the case in smll-pox), or is produced by putrefactive- changes in these discharges, as is supposed to be the case in cholera and dysentery, is also a matter of doubt. But, trout the way in which, in many cases, the organic substance is absorbed by hygroscopic substances, it appears that it is often combined, or at any rate condensed, with the water of the atmosphere."—Parkes, op. cit., p. SO. This much is known with certainty regarding the specific poisons—viz., that they differ extremely in the readiness with which they are oxidized and rendered harmless. While typhus and oriental plague throw off a poison, which, if there is due ventilation is readily destroyed, the poisons of small-pox and scarlatina spread in defiance of free ventilation, and retain their virulence for weeks or months.