36 MORPHOLOGY OF THE FORMED ELEMENTS 



continued presence in pneumonia after the crisis is further aid to 

 other clinical signs that lead one to suspect delayed resolution or 

 other complications; when accumulations of pus are suspected 

 the absence of the reaction is of very great negative value. 



BLOOD PLATES 



The blood plates or platelets in mammals are flattened, color- 

 less, very finely granular bodies, usually about one-third the di- 

 ameter of red corpuscles, that show a marked tendency to collect 

 in clumps. They are very vulnerable, changing quickly when 

 blood is drawn. On Deetjen's agar the blood plates show ameboid 

 processes. According to Wright, confirmed by Bunting, Ogata and 

 others, the blood plates are formed by detached fragments of 

 certain giant cells, the megakaryocytes (Howell), of the bone mar- 

 row and spleen. There has been a great deal of confusion as to 

 the nature of the blood plates because bodies extruded from red 

 corpuscles and somewhat similar to the appearance of the blood 

 plates may be seen in fresh blood and in films prepared in the 

 ordinary manner. The extruded bodies, however, differ from 1 rue 

 blood plates, as pointed out by Sacerdotti, by being not flattened, 

 by being homogenous and by often having a faint hemoglobin 

 tint. The blood plates may be studied in freshly drawn blood 

 diluted with physiological salt solution (0.9% NaCl solution) or 

 preferably 10% sodium metaphosphate solution which prevents 

 the clumping of these and avoids the formation of the extruded 

 bodies from red corpuscles. In fixed and stained smears the blood 

 plates take a bluish tint with eosin and methylene blue; with 

 Wright's stain the central part of the blood plate shows granules 

 of a reddish purple tint while the outer portion appears homog- 

 enous and has a bluish tint. 



Thrombocytes (spindelzellen, v. Recklinghausen), PI. Ill, 

 Figs. 2 and 9, in the blood of the domestic fowl are elliptical, oblong 

 (ii spindle-shaped cells with an elliptical to broadly oval nucleus. 

 In size the cell has nearly the length and about one-half the width 

 of the average red cell. The nucleus occupies about one-half the 

 length and nearly the entire width of the thrombocyte and is 

 usually situated in the central part of the cell. The cell body is 

 pale and often contains one or more clear vacuoles and occa- 



