In whatever way introduced the leprosy bacilli tend to invade and multiply in the lymphatics of the corium and subcutaneous tissues. In response to irritation, cells of disputed type, possibly plasma cells, appear and phagocytize the bacilli in large numbers, so that eventually the outline of the cell, as brought out in acid-fast staining, is that of a mass of red bacilli. These red-staining bodies are called _lepra cells_. In addition, endothelial cells phagocytize the bacilli and these with their bacilli, together with the free lying masses of bacilli in the lymphatic sinuses, make the so-called “globi” when seen in transverse section. The toxicity of the lepra bacillus is only slight so that we may have very large giant cells of the Langhans type and this probably explains the absence of caseation in leprosy. The arteries of the leproma, as the granulomatous mass is termed, undergo an arteritis with thickening of their walls. [Illustration: FIG. 77.—Section of spleen showing lepra cells and lepra bacilli. × 800. By permission from Manson’s Tropical Diseases.] The leproma is a mass of cells of varying sizes and types in a connective-tissue framework. The infiltrations are chiefly about the hair bulbs, sweat glands and arteries. The epidermis is separated from the leproma by a connective-tissue layer and is uninvolved except for a thinning out of the layer and obliteration of the interpapillary epithelial pegs. Incision of a leprous nodule shows a smooth glistening cut of a yellowish to slate gray color. In nerve leprosy the cellular proliferations in the region of the blood vessels and later in the perineurium and endoneurium cause pressure on the axis-cylinder with consequent degeneration. The affected nerves are swollen and reddish-gray in color. It is now thought that an axonal degeneration involves the cells of the anterior horns so that this, as well as the peripheral neuritis, is a factor in the muscular atrophies which are features of the disease. The sensory fibres are destroyed before the motor ones. Leprous changes are common in the anterior part of the eye, as of conjunctiva, cornea and iris, but rare in the posterior eyeball. The mucosa of tongue, larynx and, pharynx is often involved. Cartilage and bone are destroyed through pressure of the granulomatous tissue. The ovaries and testes may show connective-tissue increase. Nephritis is rather common in leprosy but there is considerable doubt whether the lungs are invaded by leprosy, except most rarely. Next to skin, mucous membrane and nerves, the lymphatic glands show the greatest involvement. The liver not uncommonly in nodular leprosy and more rarely the spleen may show connective tissue or cellular infiltrations. SYMPTOMATOLOGY