CYTOLOGICAL STUDIES OF LANGERHANS's ISLETS 11 



That the nuclei of the islet cells exceed more or less those of aci- 

 nus cells in bulk is evident from the figures 1 to 5. The nucleus 

 is mostly situated in the middle of the cell-body, but there are 

 cases in which it is placed near one end of the cell, which seems 

 to be dependent upon the arrangement of the cells in the islet. 

 The nuclei of b and e cells have an even contour, while those of 

 a and c and sometimes d cells are surrounded by a membrane 

 which is thrown into folds. The nuclear network, as seen in 

 the preparations fixed in osmic-acid mixtures and stained with 

 iron-hematoxylin or acid fuchsin, is most apparent in the nuclei 

 of a and d cells; that of b, c, and e cells stains more or less faintly. 

 In alum-hematoxylin preparations (fig. 23) it is seen that the 

 chromatin granules are smaller and more numerous and that 

 the network is closer in the nuclei of islet cells than in those of 

 acinus cells. Another and more important difference is that the 

 main-nucleolus of the former is always smaller than that of the 

 latter, and contains one or two nucleolini which are situated at 

 the periphery. The nucleolini are stained black by the Cajal 

 method (figs. 48 to 50), while in ordinary preparations they are 

 dissolved out so that there appear one or two small, clear vacu- 

 oles (fig. 51). In addition to the main-nucleolus, there are sev- 

 eral side-nucleoli. In contradistinction to the preparations 

 stained with iron hematoxylin, in the aium-hematoxylin prepa- 

 ration no structural differences of the nuclei between the various 

 types of islet cells can be observed. This is due to the fact that 

 the two staining methods exhibit two essentially different con- 

 stituents of the nucleus: alum-hematoxylin stains mainly the 

 chromatin, iron-hematoxylin the nucleolar substance. The 

 structural differences in the nuclei of the various types of islet 

 cells are therefore observed with respect, not to the chromatin,, 

 but to the nucleolar substance. The chromatin content of the 

 nuclei is fairly constant. Mobile the amount of the nucleolar sub- 

 stance undergoes a considerable change; this seems to point to 

 the important significance of the latter in the metabohsm of the 

 cell (Saguchi, '20). 



Mitochondria. In the study of mitochondria, the following 

 methods were applied : fixation in Meves's, Benda's, or Altmann's 



