200 HISTOLOGY 



The source of the blood plates has been known to American histologists 

 for several years, since they have had the opportunity of examining prepa- 

 rations made by J. H. Wright and described by him in 1906. The 

 specimen shown in Fig. 189 is one of several which were entrusted to the 

 writer for demonstration at the meeting of the American Association of 

 Anatomists in 1906; figures of them are reproduced in color in the 

 Journal of Morphology (1910, vol. 21, pp. 265-278). Fig. 189 represents 

 a giant cell of the bone marrow, sending out two processes or pseudo- 

 podia into a blood vessel; the endothelium is interrupted at their place 

 of entrance. By the special stain which Dr. Wright perfected, the central 

 and large part of the cytoplasm of the giant cells is seen to consist of red 

 or violet granules, identical in form and color with the granules in the 

 center of the blood plates. Moreover the giant cells are shown to have 

 a clear blue exoplasmic layer, which sends out slender processes, and 

 this exoplasm also is identical in structure with that of the blood plates. 

 Some of the blood plates are free in the vessels; others in rows or clumps 

 are still connected with the giant cells. Fig. 189 shows a few detached 



FIG. 189. GIANT CELL FROM THE BONE MARROW OF A KITTEN. SHOWING PSEUDOPODIA EXTENDING INTO 

 A BLOOD VESSEL (V). AND GIVING RISE TO BLOOD PLATES (bp). (J. H. Wright.) 



plates, and one which is budding off from a pseudopodium, but the color- 

 contrasts which make these preparations convincing are scarcely indicated. 

 Through Wright's investigations it has been made clear that blood plates 

 are detached portions of the cytoplasm of the giant cells in the bone 

 marrow, and of similar giant cells in the spleen; their granular center is 

 endoplasm, and their hyaline border is exoplasm. 



According to Schafer (1912) Wright's "suggestion" seems improbable; and the 

 blood plates may be looked upon as minute cells. Others also have regarded the gran- 

 ular endoplasm as a nuclear structure. The blood plates are still described by many 

 writers as fragments of disintegrating white corpuscles, or fragmenting nuclei of red 

 corpuscles; and Stohr records that their origin is obscure. 



