So little is known concerning blood-platelets, and so little interest has been taken in them, that their description by Adami and Nichols1 is almost fully quoted. If only because they play so important a part in the process of thrombosis it is necessary to have a clear understanding regarding the blood-platelets, or, more accurately, regarding what is known concerning their origin. Apart from this, since the advent of the Romanowsky stain and its modifications, they have of late years come in for increasing recognition. There is no longer any disposition to regard them as artefacts, but there is still dispute as to their exact significance and as to their unity or duality. They are small bodies of varying size, in general about 2 μ in diameter, oval or pear-shaped, evidently labile, and varying in shape with slight compression by neighboring cells or platelets, tending to be present