THE RATE OF REGENERATION OF BLOOD PLATELETS.

By repeatedly withdrawing, defibrinating, and reinjecting blood, the platelet count in dogs can be reduced to an extremely low level. When the reduction in platelets and fibrinogen has been carried to an extreme degree the animals display a marked tendency to bleed. The regeneration of platelets after their removal by defibrination is remarkably rapid and amounts, on an average, to about one fifth of the entire number in the blood per day. From the experiments and from observations on the platelet count in human beings, it is believed that under the usual conditions of life platelets are utilized or destroyed and replaced in enormous numbers daily, and that the life cycle of the platelet is extremely short,-possibly a matter of a few days.