CYTOLOGICAL STUDIES OF LANGERHANS's ISLETS 27 



apposition, the both ends of the cell being in contact with the 

 membrane which encloses the cord. There are, however, cells 

 which end freely before reaching the membrane of the opposite 

 side; this is dependent, in part at least, upon the direction in 

 which the section is carried through the cords. Cases in which 

 the cells of the islet show no regular arrangement may also be 

 due to the same cause. It sometimes happens that two cords 

 run side by side, separated only by the connective-tissue mem- 

 brane (fig. 6). My observations show that all typical islets, 

 however diversified they may appear, consist of a system of cell- 

 cords which intertwine with blood-capillaries. 



The typical islets usually consist of cells already mentioned. 

 In most of the islets, especially in the larger ones, the e cells are 

 the most abundant, although the h cells may sometimes exceed 

 them in number, especially in the smaller islets, while a, c, and d 

 cells are few in number or entirely lacking (fig. 1). As regards 

 the position of these different types, it can generally be said that 

 the h cells are situated at the periphery of the islet so as to form 

 a sort of cortical layer. As is the case with the non-typical islet, 

 the e cells are here, too, separated from the neighboring acinus 

 cells by h cells. In addition, the h cells not infrequently are of 

 such a form and arrangement as to suggest compression from the 

 acinus tissue, d cells, if present at all, are almost always inter- 

 posed between the e cells, while a and c cells are located at the 

 periphery of the islet. The e cells lie in contact v/ith the blood- 

 capillaries, which is not always the case with h cells. 



The typical islets are, in the majority of cases, larger than the 

 non-typical ones, and may be found everywhere in the pancreas 

 except in the peripheral layer, the largest ones being located gen- 

 erally near the center of cross-sections of the pancreas. 



It follows from the above observations that the pancreas con- 

 tains either solitary islet cells or groups comprised of few or 

 many cells. These cell groups may be subdivided into non- 

 typical and typical islets. Most of the islet cells belong to the 

 e and h type, while a, c, and d cells are few in number. The e 

 cells form an essential constituent of the typical islet, whereas h 

 cells are usually isolated or occur in small groups. Solitary cells 



