X-ray showing lungs affected by fibrosing alveolitis. This is a condition in which the alveoli, tiny air sacs in the lungs, become inflamed and thickened. The elasticity of the lungs during breathing is reduced as well as the efficiency of gas transfer between the lungs and the surrounding blood vessels. X-ray examinations of lungs affected by fibrosing alveolitis show a diffuse fine or coarse pattern which is here clearly visible at the base of the left lung (bottom right) and close to the trachea. This disorder is commonly caused by an allergic reaction to inhaled dust of plant or animal origin and is treated with corticosteroid drugs.