Thin section of a platelet from a sample of washed cells incubated with Fgn/Au particles for 15 minutes, then exposed to 5 U/mL of thrombin for 60 seconds before fixation in glutaraldehyde-tannic acid-osmium to selectively stain the platelet glycocalyx, fibrinogen, and fibrin. This example is one of several serial sections through the same platelet. It and the other serial sections show the typical features of shape change and internal transformation caused by thrombin. Fgn/Au particles are bound to the irregular surface and are in the process of entering channels of the OCS. The OCS channel indicated by an arrow (↑) is filled with fibrinogen and fibrin stained by tannic acid-osmium black. The tortuous channel is connected directly to several  granules (G₁, G₂, G₃) in various stages of labelization. Residual fibrinogen is stained by the reaction product. Fgn/Au particles carried by the OCS have entered the  granules (G₁, G₃, G₄). The direct connections between OCS channels and  granules in this example and its serial sections is indisputable. Original magnification ×45,000. (Reprinted with permission.19)