Platelet Economy (Platelet Survival and Turnover)*

I nvestigators studying blood platelet survival and turnover have used the term ‘thrombo‐kinetics’ to describe the subject, by analogy with the usages of thermodynamics. Inasmuch as these phenomena reflect the interactions and hazards which the platelets encounter while discharging their function in the circulation, we prefer the term ‘platelet economy’ and we consider that the function and fate of the platelet cannot usefully be separated as objects of study. A number of beliefs about platelet function and economy are widely held. First, the platelets play a leading role in haemostasis, a function which is discharged mainly when injury to the vessel wall occurs; their second main function is considered to be in coagulation, which they support or may even initiate. Beyond these, the platelets are thought to have little useful function. The platelet in vivo is commonly supposed to be a fragile structure, irreversibly damaged by aggregation. Some consider it to have a finite life span, determined by exhaustion of its inner reserves, while others consider its life span to be determined by the demands of the body without regard to the age of the individual platelet. We shall present evidence suggesting that some of these views are gross over‐simplifications and some are erroneous.