BLOOD PLATELETS 



43 



BLOOD PLATELETS 



The author (Aggeler) is aware of the 

 fact that the platelet counts reported 

 by him and his associates could be 

 higher than those observed by Tocan- 

 tins and Sloan because certain arte- 

 facts were consistently counted as 

 platelets. On the other hand there is 

 no proof that the latter authors did 

 not mistake some of the platelets for 

 artefacts. It is begging the point to 

 demonstrate that any single observer 

 may obtain consistent results. This 

 means only that he is constant either 

 in identifying platelets as platelets, 

 platelets as artefacts, or artefacts as 

 platelets. It does not prove that the 

 particular observer is always identify- 

 ing platelets as platelets and artefacts 

 as artefacts. Furthermore, the fact 

 that several observers using the same 

 naethod may obtain reasonably con- 

 sistent results does not prove the valid- 

 ity of the method, since both observer 

 may be committing the same error. 

 The ultimate cause for the great varia- 

 tion in the reported results of different 

 observers using the same method is 

 that platelets cannot be distinguished 

 from artefacts with certainty in any 

 method in which the magnification and 

 resolution is not considerably better 

 than that which can be achieved with 

 the high dry lens and bright field il- 

 lumination. Some improvement can 

 perhaps be gained by the use of dark 

 field illumination, as recommended by 

 Scheff and Ralph (Am. J. Clin. Path., 

 1949, 19, 1113) or by the use of phase 

 contrast illumination, as advocated 

 by Brecher, G. and Cronkite, E. P. 

 (J. Applied Physiol., 1950, 3, 365). 



Nothing is gained by the use of ocu- 

 lars giving a magnification greater 

 than lOX since, in the absence of any 

 mprovement in resolution, the in- 

 creased magnification only serves to 

 increase the confusion. Attempts have 

 been made by Helber, E. (Arch. f. 

 Klin. Med., 1904, 81, 316) and by 

 Maixner and Von Decostello (Med. 

 Klin., 1915, 11, 14) to increase magnifica- 



tion and resolution by the use of the 

 Zeiss D water immersion lens. With 

 this equipment, magnification of lOOOX 

 was attained. Approximately the same 

 magnification with better resolution 

 can be achieved with an oil immersion 

 lens. However, with these lenses, it is 

 necessary to use a specially constructed 

 counting chamber of 0.02 mm. depth 

 and a cover slip not more than 0.25 mm. 

 in thickness. Because of the reduced 

 depth, a 1 to 40 dilution of blood is 

 used in order to obtain the same num- 

 ber of cells per unit area of the counting 

 chamber as are present when using a 

 1 to 200 dilution in the 0.1 mm. depth 

 chamber. The author and his associ- 

 ates have found no difficulty in dis- 

 tinguishing artefacts from platelets 

 with a chamber and coverslip of this 

 type* used in conjunction with a Spen- 

 cer binocular microscope equipped with 

 1.8 mm., 97X (oil immersion) N.A. 

 1.25, medium dark contrast phase ob- 

 jective, standard condenser lower ele- 

 ment, standard N. A. 1.25 condenser 

 top element, 97X annular diaphragm 

 and lOX Hugenian eyepieces. Even 

 the morphologic characteristics of small 

 platelets were clearly visible. Most of 

 the platelets appeared as flat, round or 

 oval discs, about 2 microns in diameter 

 and 0.5 microns thick. The cytoplasm 

 showed a uniform, fine granulation. 

 Some of the platelets had a slightly 

 irregular shape, most had a single short 

 slightly curled filament, others had 

 more than one filament, and a few had 

 none. Occasionally two platelets at- 

 tached by a long streamer of cytoplasm 

 were observed. Rarely was an "explo- 

 sive" degeneration form of platelet 

 seen, and none of the platelets had the 

 multiple sharp spinelike projections 

 which always appear when no fixative 

 is employed in the diluting fluid. The 

 principal artefacts observed were bits 

 of amorphous debris which could be 

 distinguished by their irregular shape 

 and heavy granulation; erythrocyte 

 fragments, which were colored yellow, 

 had no granulation and were intensely 

 refractile; and clumps of bacteria, 

 which were identified by their regularly 

 spaced heavy granules separated by 

 fine dark filaments. Unfortunately, 

 while the problem of differentiation of 

 platelets from artefacts is solved by this 

 systern of microscopy, extreme differ- 

 ences in the platelet counts on aliquots 

 of the same venous blood specimen were 

 encountered, so that the advantage of 



• Manufactured by the American Optical Co., Buf- 

 falo, N. Y., through the courtesy of Mr. C. E. Guellich, 

 Manager of Product Salea, Scientific Division. 



