In 1882, Bizzozero,1 an Italian pathologist, first described platelets as they appear in small blood vessels and demonstrated their adhesive quality, their participation in thrombi, and their role in blood coagulation. Progress did not soon follow these astounding contributions. Only during the past 15 years has an explosion of interest and knowledge in platelets and their disorders been witnessed. It is now known that platelet structure, metabolism, and function are all important in the participation of platelets in hemostasis and that abnormalities in these can lead to specific bleeding disorders of varying severity.
Structural physiology has gradually become a precise science. Different zones and various organelles in the platelet body have now been related to well-defined platelet functions. The so-called platelet storage granules have intrigued investigators for years, and only recently has their role been clarified. Two types of storage granules are present within platelets—the alpha granules and the