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IN DISCUSSING -hazardous particles, the distinction offers a fair standard. between dust, fumes, smoke and mist is frequently ^overlooked. Drinker and Hatch' state that dust is Table II. formed by reducing earthy materials to small-sized Permissible Dubt Concentrations in Various Industries portions, sub-micro3copic to the visible, the compo sition of the particles being the same as that of the parent material. Common examples are the mineral Induct ry PeteenUf* SUiea is the Du,l Perraieeihle Duet Coceeotnttoa Mince per Cable tiat dusts derived fromthe disintegration of rock and the organic dusts like wheat and flour. Fumes are formed by processes like combustion, sublimation and condensation. The particle size. is generally below 1 micron. Smoke is generally of organic origin and is char So-itb Alrio*....................... OflUrio Cold MiMt*........... AuetralU SnadcW&e*........... GnxUt**.,,................. Pe&neytouia Aathmdte Cod Mine***. IS 13 6 Broktti fllU* Attttrmli**........ 00 tn t0 S to 10 10 to IS *0 14 acterized by a particle size below 0.5 microns. EUttd ttpotk ttfiowiflc practice. Mists or fogs are formed by the condensation of ______upon djpicwi tudin. _ water vapor upon suitable nuclei. The particle or drop Of the dusts studied up to the present time, only let size varies widely, depending on the condition silica and asbestos produce definite pulmonary fibrosis. prevailing. All the other types of pneumoconiosis exhibit the same The significance of these distinctions becomes ap general kind of tissue change with a similar pattern parent when evaluating the exposure in an individual of shadows on the roentgenogram. Gardner states that manifesting signs or symptoms of pneumoconiosis. the pattern in this instance consists of a mere accen Since men working in dusty atmospheres are fre tuation of the normal branching, tree-like shadows cast quently exposed to a combination of these factors, the chiefly by the pulmonary blood vessels. It represents a actual cause of fibrosis may be obscured, a fact which simple benign type of linear fibrosis and is difficult to has considerable importance in cases involving litiga distinguish from the mild accentuation of linear mark tion. ings sometimes seen in x-rays of individuals with no Like "rheumatism," the term "pneumoconiosis'* known history of dust exposure. covers a variety of conditions. It has been defined as Various terms are used to indicate special types of a "chronic pulmonary fibrosis due to the inhalation of pneumoconiosis. For instance, "anthracosis" desig irritating dusts which produce a proliferative reac nates a condition of the lungs found among coal miners tion" (Johnson*), or a condition due to "the effects due to the inhalation of coal dust. "Siderosis" de upon the lungs of the inhalation of excessive quantities scribes the tissue reaction occurring in some iron ore of dust, manifested by structural changes in the lung miners, and such terms as "byssinosis," and "tobac- tissue and entirely distinct from the action of poison osis" refer to the pulmonary changes resulting from ous dust such as lead or mercury, in which case the exposure to dust from cotton and tobacco. While such lungs act merely as the point of entrance into the body distinctions do not add much to our knowledge of dis without definite local influence" (Pancoast0). Perhaps eases due to dust, nevertheless it is desirable to have a the simplest way of stating it would be to say that the general conception of the important physical and terra refers to a condition of the lung3 resulting from roentgenological features of each for the sake of diag the prolonged inhalation of dust whether harmful or nosis. inert. In this connection it is advisable to mention the Pneumoconiosis includes such specific diseases as status of the silicates. The term "silicatosis" has been anthracosis, asbestosis, siderosis, silicosis, etc. used from time to time to describe changes observed in the chest x-ray of persons exposed to dust from TM RECENT years few diseases have received more at- such substances as talc, soap stone, mica, feldspar, tention and publicity than those due to dust The garnet, etc.; but the exact role played by these silicates work of the United States Bureau of Mines in the in the production of pulmonary change has not yet Tri-State Lead and Zinc Mining districts (1924-1927) been definitely established. They constitute a group of and the Metropolitan Life Insurance Company7 di numerous minerals which find widespread use in in rected attention to other industries where disabling dustry, but with the exception of asbestos, their pulmonary diseases were known to exist- Other inves capacity to produce fibrosis has not been demonstrated. tigations were* made by the U. S. Public Health Petrologists warn against the potential hazard from Service, and in 1933 Gardner and Cummings, of the silicates but experiments so far have produced no evi Saranac Laboratory, began extensive studies in the dence of connective tissue proliferation as a result of iron ranges of Northern Michigan, and Wisconsin. their use. On the other hand, it should not be assumed Since that time, many industries, here and abroad, that lack of such evidence indicates absolute i> xrtneas. have established clinics and laboratories for further The changes observed in the chest x-rays of persons, research and control of the hazard. exposed to silicate dust have been theoretv :ally ex The pathology of these diseases was definitely estab plained as a mild silicosis arising from silica ieft after lished by Dr. Leroy U. Gardner,* Director of the Sara the body fluids have leached the bases out of the sili nac laboratory, in 1934. He demonstrated the effects cotic molecule. A representative group of 24 silicates of various dusts on the lungs of laboratory animals and used in industry, listed by Gardner, appears in Lanza's studied the part played by tuberculosis in the progress book, "Silicosis and Asbestosis." The inert duats, of the disease. The etiology, physical signs and symp which include most of the silicates, are relatively un toms, x-ray and laboratory findings were fully de important because of their non-disabling character. scribed and many other details of a technical nature A few of these materials are limestone, marble, talc, determined. During this period also, concentration chalk, calcined magnesium for insulation, furnace lin codes, representing "safe" limits of air borne dust, ings, carbon dust, iron dust, tobacco dust, cement, were recommended. These vary in different locations cotton, molds, fungi, etc. but, generally speaking, the following table, set up by Anthraco-silicosis results from excessive exposure to the Committee on "Prevention of Silicosis Through coal dust which contains amounts of free silica. Since Medical Control" of the National Silicosis Conference, carbon is one of the inert dusts, it seems reasonable SPNY 000229