PURPURA  , in

pathology, a general term for the symptom of purple-coloured spots upon the surface of the body, due to extravasations of blood in the skin, accompanied occasionally with haemorrhages from mucous membranes . The varieties of purpura may be conveniently divided as follows: (a) toxic, following the administration of certain drugs, notably copaiba, quinine, ergot, belladonna and the iodides; also following snake-bite; (b) cachectic, seen in persons suffering from such diseases as tuberculosis, heart disease, cancer, Bright's disease, jaundice, as well as from certain of the infectious fevers, extravasations of the kind above mentioned being not infrequently present; (c) neurotic; (d) arthritic, which includes the form known as " Purpura simplex," in which there may or may not be articular pain, and the complaint is usually ushered in by lassitude and feverishness, followed by the appearance on the surface of the body of the characteristic spots in the form of small red points scattered over the skin of the limbs and trunk . The spots are not raised above the surface, and they do not disappear on pressure . Their colour soon becomes deep purple or nearly black; but after a few days they undergo the changes which are observed in the case of an ordinary bruise, passing to a green and yellow hue and finally disappearing . When of minute size they are termed "petechiae" or " stigmata," when somewhat larger " vibices," and when in patches of considerable size " ecchymoses." They may come out in fresh crops over a lengthened period . Purpura rheumatica (Schonlein's disease) is a remarkable variety characterized by sore throat, fever and articular pains accompanied by purpuric spots and associated with urticaria and occasionally with definite nodular infiltrations . This is by many writers considered to be a separate disease, but it is usually regarded as of rheumatic origin . Purpura haemorrhagica (acute haemorrhagic purpura) is a more serious form, in which, in addition to the phenomena already mentioned as affecting the skin, there is a tendency to the occurrence of haemorrhage from mucous surfaces, especially from the nose, but also from the mouth, lungs, stomach, bowels, kidneys, &c., sometimes in large and dangerous amount . Great physical prostration is apt to attend this form of the disease, and a fatal result some-times follows the successive haemorrhages, or is suddenly precipitated by the occurrence of an extravasation of blood into the brain . (see above) by the action of aqueous ammonia at 15o° C . It also results instead of the expected 7-methyl-2-oxy-6-aminopurin, when 7-methyl-6-amino-2-chlorpurin is treated with dilute alkalis (E . Fischer, Ber., 1898, 31, p .

542), owing to

ring splitting in the 1.6-position, followed by eliminating of halogen acid . Thiopurins.—W . Traube (Ann., 1904, 331, pp . 66 seq.) has obtained many compounds of the purin group by using thiourea, which is condensed with cyanacetic ester, &c., to form thiopyrimidines .