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iment, and happily the harriers were not then existing and the obstacles to research had not been devised. With all these observers from the commencement the unfolding of medical science has been a gradual one, as step by step the darkness of ignorance was dispersed by increasing knowledge.
It is the object of science to attain to exactness in knowledge, and the advance of one line of truth reacts upon others in close relation with it; during later years how much has been ascertained as to the character of the blood itself, its more precise composition in varied periods and states of health, not only as to its white corpuscles and the red corpuscles, and perhaps other forms, but as to the migratory character of the leucocytes; chemical science has unfolded much and will do still more, but the microscope and the spectroscope have added immensely to our knowledge in relation to the pathological, as well as the physiological changes of the blood itself. With a better knowledge of the heart and its valves, and
