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The phenomenon of agglutination and fusion of the blood plate. lets into glassy masses and strands, as observed in films of wet blood between a slide and cover-glass, was first described by Hayem (1) in 1878. Some years later, it was more exactly described by Bizzozero (2) and named "viscous metamorphosis" by Eberth and Schim. melbusch (3). It occurs during the process of coagulation and is weU marked at the time of the first appearance of the fibrin threads. It does not take place if sodium oxalate or certain other salts have been added to the blood during the bleeding in sufficient amount to prevent coagulation and if other conditions are favorable. Mosen (4) in 1893 was the first to show that platelets from such a noncoagulating blood, freed from blood elements by centrifuging, do not fuse with one another, but retain their separate identity. They appear when in suspension in isotonic salt solution and observed with medium powers between a cover-glass and slide, as refringent, glistening granules or round bodies of a diameter varying approximately from one-fourth to one-half that of a red blood corpuscle (Fig. 1); they are not clumped but uniformly distributed and remain so until they disintegrate. We have found, however, that such platelets normally have not lost the ability of metamorphosis, but that they undergo the characteristic changes within a few minutes if serum or certain more or less closely related substances are added to the suspension. As observed under the conditions just mentioned, the platelets begin their metamorphosis by aggregating and agglutinating in masses and strands which increase in size up to a certain point within a few minutes. Then within a few more minutes, the plate-395 on

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A megacaryocyte is seen commonly as an occasional cell in the peripheral blood of patients with myelogenous leucemia. Less commonly they appear in relatively large numbers. These giant cells also may occur in the blood under other conditions. Their presence is indicative of a bone marrow under intense strain.