Representative light micrographs of blood-collagen interactions. The surface was exposed at a shear rate of 2,600 s⁻¹ during 3 minutes to nonanticoagulated blood drawn from volunteers given either placebo (A), aspirin (B), ticlopidine (C), or the combination of both (D). The sections were prepared perpendicular to the direction of the blood flow. Note that the collagen coat is not visible because the staining procedure does not contrast the fibrils. Original magnification × 1,000. Bar represents 10 μm.