J. clin. Path. (1948), 1, 175. THE ENUMERATION OF BLOOD PLATELETS BY

The platelets of human blood can, with reference to their fragility, be divided into two groups. The first group comprises the smallest platelets with very high fragility described for the first time by Floessner (1922). In the second group are the medium-sized and large platelets which have a higher degree of resistance and show in normal individuals a typical curve of disintegration (Baar and Szekely, 1929). The existence of the first group was questioned by Hartmann (1932), who regarded the tiny platelets as fragments of normal blood cells. Steinmaurer (1932) was, however, able to demonstrate by a special method this type of platelet in stained films (compare also Juergens, 1934). Apart from these platelets of normal people, there are also pathological giant forms (found especially in thrombocytopenic purpura) and exceptionally highly resistant pathological micro-platelets. The latter form was seen by Baar (1934) for a short period in a case of essential thrombocytopenia. Corresponding to the two main types of plate-lets the technical methods for their enumera-tion may be divided into two groups. Thus the methods of Floessner (1922), Boshammer (1926), Juergens (1934), Steinmaurer (1932), Cumings (1933), and Olef (1935) permit the enumeration of all platelets, and the number found in normal individuals by these methods is 700,000 to 900,000 per c.mm. All these methods, however, are very laborious and unsuitable for routine laboratory work. Moreover, up to date no pathological con-ditions are known in which only the number of the most fragile platelets is decreased or increased without corresponding changes in the other groups of platelets. The much simpler methods of the second group supply us, therefore, with sufficient information. These are either indirect, in which the number of platelets is calculated from their relation to red blood corpuscles in stained ifim