In the present light of pathological science it is impossible to answer this question in the affirmative without considerable qualification. It must be confessed that we do not possess a knowledge of any definite chain of morbid processes constituting a distinct disease that may be designated as purpura. And yet we are able to recognize a set of symptoms varying greatly in intensity, from the most trivial petechial eruption to profuse and fatal hemorrhages, accompanied by a train of manifestations which we are unable to connect with any of the causes already spoken of, and which, indeed, depend upon no fixed exciting cause with which we are acquainted. It may be eventually proven that purpura, even as we understand it, is merely a set of phenomena due to widely-differing influences acting upon the blood and blood-vessels, and that the term will disappear from our nomenclature as indicating a disease, but will be preserved as denoting a symptom. For the present, {187} purpura is understood to be a group of symptoms characterized by the effusion of blood into the tissues of the body, or upon its free surfaces, or into its serous cavities, which seem to arise spontaneously, and for which we are unable to assign a definite cause. With this view of the nature of purpura it becomes necessary to exclude from present consideration blood-extravasations from internal or external violence, the action of the specific principles of contagious or infectious fevers, the dyscrasia of scurvy, the influence of poisonous substances, and, in a word, any of those affections of which the escape of blood from the vessels constitutes an epi-phenomenon. Purpura may be conveniently considered as presenting three varieties: 1, purpura simplex; 2, purpura hæmorrhagica; 3, purpura rheumatica. These three forms of the disease are not distinguished by sharply-outlined differences, but merge the one into the other, now one, now another set of symptoms predominating. To these may be added, likewise for convenience, three sub-varieties--purpura urticans, purpura papulosa, and purpura nervosa. The difference between these forms of purpura should not be considered as of more than clinical import. Whatever variations present themselves may with probable propriety be ascribed to complicating influences.