Viscous metamorphosis of platelets has been studied with the light microscope, and ultra-thin sections have been prepared at progressive stages for examination in the electron microscope.

The phase contrast light microscope reveals rapid aggregation and distortion of platelets and gives the impression of their fusion into structureless aggregates during viscous metamorphosis.

Sectioned material collected during viscous metamorphosis of platelets and examined in the electron microscope reveals a remarkable degree of retention of structure in a majority of the platelets. All become deficient in granules and devoid of vesicular spaces, but most retain intact cell membranes, and the structureless masses seen with the light microscope are found to consist of densely aggregated platelets. Fusion and complete loss of identity occurs in the minority.

The retracted clot was found to contain densely aggregated, distorted and elongated platelets, empty of granules and intimately related to fibrin particles.

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