HISTOGENESIS OF BLOOD IN BUFO HALOPHILUS 223 



Small lymphocytes. A few typical small lymphocytes (fig. 7, s.lc) 

 are seen in the 16-mm. stage and more in later stages. These cells 

 have proportionately large nuclei and a narrow rim of basophil 

 cytoplasm. The chromatin is disposed in large angular blocks, 

 some typical 'Radkern' or wheel-like nuclei being found, but no 

 nucleoli may be distinguished. 



Transition stages from large to small lymphocytes are found. 

 It is evident that the small lymphocyte is a more highly differ- 

 entiated cell form than the large lymphocyte, for when the latter 

 differentiates to a granulocyte similar changes in the nuclear 

 constitution occur, the chromatin becoming more abundant and 

 the nucleolus disappearing. 



Eosinophil cells. These cells, in the mature state in which they 

 are found intravascularly, possess horseshoe-shaped, lobed, or 

 segmented nuclei, cytoplasm which takes very little stain with 

 eosin-azure II, and many coarse round eosinophil granules of 

 varying size. The nuclear chromatin is larger in amount than 

 in the large lymphocyte, but is still quite variable, being disposed 

 primarily in contact with the well-defined nuclear membrane 

 and then in variable density over the nuclear network. In this 

 network no nucleolus can be distinguished. The karyoplasm is 

 clear and almost colorless to eosin-azure II. The larger oxyphil 

 granules often show a clear area in the center, staining more 

 deeply peripherally, while in other cells smaller, more deeply 

 staining, homogeneous granules occur. These granules become 

 very numerous in mature cells, which may occasionally show 

 mitotic figures. Such cells may readily be found in all phases of 

 diapedesis from the tissue into the vessels. They are also found 

 in the circulating blood. In one isolated but unmistakable case 

 (fig. 7, e.end) an eosinophil cell was found as a part of the endo- 

 thelial wall itself. 



All transitions from typical large lymphocytes to mature 

 eosinophil leucocytes are found. First a few coarse basophil 

 granules, which, however, show no trace of metachromasia, 

 appear, usually in the concavity of the slightly indented nucleus, 

 soon increasing in number and changing their stain from blue to 

 purple red with eosin-azure II; then the nuclear membrane 



