At the outset it may be desirable to give a brief outline of the phenomena upon which this work is based.

A complete historical survey takes us back to very early times, to the days of Hippocrates and in more recent times to the humoral pathologists, when the formation of the “crust phiogistica” or “buffy coat” was practically the only blood symptom known. Until the old humoral theories were discarded, that is until the rise of the doctrines of cellular pathology, the problem loomed large, but after this period interest in it declined, until the whole matter was revived about ten years ago by R. Fahraeus, of Stockholm, who published a series of researches into what he termed the “suspension stability” of the blood. By this term is meant the power which the plasma has of holding the erythrocytes in suspension. When the stability is lowered, the corpuscles sink with increased rapidity. This author found that a lowered suspension stability occurred in a large number of morbid conditions, and also in one physiological condition, namely pregnancy. Since the publication of this work the phenomenon in question has been made the basis of a test which has found considerable application in certain departments of medicine, notably in gynæcology and tuberculosis.