Extravasation of blood into the superficial layer of the true skin is described as purpura. The hemorrhage occurs as a consequence of some change in the composition of the blood, excessive pressure of blood in the email vessels, or impairment of the functions of the nerves which regulate their calibre. The lesions or blood-stains in the skin may be in the form of spots, small or diffused patches, or marks which look like bruises. The discoloration, it should be noticed, is the result of diffused blood and not merely of congestion. Pressure applied to the latter completely removes it, but it does not remove the discoloration by blood when extravasated. As the cause of the extravasation is some serious derangement of the system, the disease is not to be dealt with by local remedies. (See Purpura Haemorrhagica.)