Friction sounds.—When the surfaces of the pleurae have
become rough by disease, a sound is produced as they move
over one another during respiration. This is called a " friction
sound." It may vary in intensity from a sound which is barely
audible, to one that is very loud. It may be heard during
inspiration or expiration, or with both, and may present the
characters of grazing, rubbing, or creaking, &c.
CHAPTER I.
DISEASES OF THE PLEURA AND LUNGS.
Pleuritis.-Pleurisy; Inflammation of the Pleura.—Acute, chronic, general, partial, primary, secondary.
Inflammation is more common in the pleura than in any other tissue or organ ; its effects (adhesions) being found after death in the greater number of persons. It may be general or partial, associated with disease of the lung, or secondary upon that of other organs, as of the kidney or heart. In most cases it affects one only, and most frequently the right side of the chest ; but occasionally both pleurse are involved.
Anatomical characters.—In the early stage the pleura is redden- ed in dots, points, or streaks, and its brilliancy is lost. The sur- face is covered with a layer of lymph, which, in sthenic persons, resembles thick cream, but in asthenic persons is more serous and less plastic. Serous fluid, clear or turbid, accumulates in the sac. In the progress of the disease, exudation becomes more abundant, and undergoes various changes : thus, it may be completely organized into delicate areolar tissue by which the surfaces adhere, or, the organization being less per- fect, it separates as flakes or films which float in. the fluid and render it turbid. Lastly, being insusceptible of organiza- tion, it is converted into pus. In asthenic persons, the lymph is caco-plastic, accumulates in successive layers of considerable thickness, and becomes coarse fibrous, or fibro-cartilaginous tissue, into which calcareous matter may be deposited. When the quantity of fluid is small, the parietal and visceral layers are
