The two chief characteristics of the blood platelets are their marked tendency to undergo speedy dissolution in shed blood and their property of adhering to one another and to foreign objects. These characteristics explain the difficulties that have been experienced in attempts to count accurately the number of platelets.
The early investigators used various preserving fluids in their attempts to prevent the disappearance of the platelets from freshly drawn blood, and the counts were made with the ordinary hematocytometer. The results were regarded as so unsatisfactory by Halla1 that he concluded from his study that it was impossible to determine the absolute number of blood platelets, and that the relative number could be estimated best in fresh preparations. Only a few years ago Türck2 employed the same procedure, evidently because he regarded even the newer methods of counting the platelets as quite untrustworthy. The investigations of Eberth and