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 system. And from this point of view, while duly appreciating the results of scientific researches, the fact cannot be too strongly insisted upon at the present day that, after all, the great bulk of our knowledge respecting these conditions, as well as our ability to deal with them on sound and rational principles, has been derived from the ordinary methods of investigation, which are more or less within the reach and scope of every practitioner. These methods include intelligent inquiries bearing upon the ætiology and pathology of the various affections; the routine performance of post-mortem examinations in hospitals, and the systematic study and teaching of morbid anatomy and histology; clinical investigations and observations on living subjects, on an extensive scale, not only in hospitals but also in general practice; and the methodical and careful study of the effects on individuals of therapeutic agents and measures, both in health and disease. It is only within comparatively modern times that investigation on these lines has been properly developed and established, and the greater part of our positive and reliable knowledge of affections of the circulatory system has been thus acquired during the nineteenth century, especially during its latter half. Of course, the study of morbid histology as now carried out is quite of recent date, and it has undergone remarkable development within the memory of most now