HISTOGENESIS OF BLOOD IN BUFO HALOPHILUS 225 



The mast cells are mostly extravascular ; one or two only being 

 found within the vessels in my preparations, and are very few in 

 number, not more than one occurring in each section. 



The nuclei are simple, round, oval, or bean-shaped. In the 

 younger stages the nucleus is that of a large lymphocyte, round 

 and .clear, with but little chromatin in small karysomes, and a 

 metachromatically basophil nucleolus, the cytoplasm is broad 

 and usually slightly basophil, the granules are large, round, and 

 comparatively few in number, staining an intensely dark purplish 

 blue with eosin-azure II and violet red to blue violet with thionin. 

 No variation in the staining quality of these mast granules could 

 be found in any stage of their development. Thus the possibility 

 of confusing the younger eosinophil granules with mast granules 

 is excluded. In the older cells (fig. 7, m.c) the cytoplasm becomes 

 less basophil, the mast granules increase in number, the nucleus 

 becomes richer in chromatin, the nucleolus changes its staining 

 quality and becomes indistinguishable from the chromatin. In 

 some cells the chromatin is disposed in a typical 'Radkern,' being 

 distributed in large angular blocks lying against the nuclear 

 membrane and pointing toward a centrally located one. The 

 karyoplasm is clear and may be slightly oxy- or basophil. Trans- 

 ition stages between these two types, here designated as older 

 and younger, are seen. One cell, manifestly an old one, was 

 found, in which the chromatin was decreased in amount, the 

 nucleus appearing vesicular, the cytoplasm was colorless and 

 showed ragged edges, indicating fragmentation of its periphery. 

 In this cell the granules were large, only about six or seven re- 

 maining. Some evidence of amoeboid activity may be noted in 

 the contour of many of the mast cells. 



Special cells. Under this head are designated many cells 

 with purplish-pink cytoplasm and simple to polymorphous nuclei 

 (fig. 7, s.c). The more polymorphous of these nuclei may be 

 lobed and segmented, as many as five lobes being found. Their 

 chromatin is more or less abundant and lies along the nuclear 

 membrane and in a chromatin net, or in small karyosomes in 

 faintly oxyphil or colorless karyoplasm. The cytoplasm is the 

 homogeneous, indistinctly granular, or, in a few cases, definitely 



