If there be a peculiar morbid process having for its constant and characteristic symptom the spontaneous escape of the blood from the blood-vessels, it is plain that interstitial hemorrhage from external violence or from the action of a definite poison circulating in the blood and disorganizing it and its containing vessels, as in phosphorus-poisoning, or from the influence of certain zymotic diseases, should not be designated by the title properly belonging to a substantive malady. The question, therefore, is: Are there groups of symptoms indicating morbid action of definite character, but of varying intensity, to which the name purpura may with propriety be applied?
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.