ACQUIRED DISEASES FROM DUSTS.
The first class of physical agencies by which diseases of the body are acquired may be included under the term " dusts." In this term we comprise those particles of solid matter which are mechanically suspended in the air, which settle on the body, which sometimes affect the eyes, and which are inhaled in breathing.
It is through the breathing organs, the lungs, that these dusts are most productive of injury; and it is among the industrial classes of the community that the injury produced is most fre quent.
Dusts mechanically drawn into the lungs may induce true organic mischiefs, some of which, as we shall see, are of fatal character, although as a rule they are purely local in respect to their primary action on the body.
The dusts that inflict injury are of varied quality. They are also of varied effect in regard to the specific evils which they pro duce. We shall most conveniently study them as divided into different groups, according to their physical characters, as fol lows: (a) Cutting dusts, formed of minute hard, crystallized parti cles which have sharp, cutting, and pointed edges. These dusts are composed of iron, steel, stone, sand, glass, dried silicates of earthen-ware, lime, pearl.
(b) Irritant dusts, derived from woods; from ivory; from textile fabrics, such as fluffs of wool, silk, cotton, flax, or hemp; from hair; from clay. Soluble saline dusts, derived from soluble crystalline substances.
(c) Obstructive and irritating dusts, composed of carbon, of fine particles of coal dust, of soot, of rouge, and of flour.