CYTOLOGICAL STUDIES OF LANGERHANS's ISLETS 35 



t eristic of acinus cells. They cannot be regarded as acinus cells 

 in the resting state, since the resting cell, besides still containing 

 some zymogen granules, has a large nucleolus and a great number 

 of thick mitochondrial filaments. 



From these observations I have been led to the conclusion 

 that the transformation of islet cells into acinus cells takes place 

 in the following manner: First, the cytoplasm of the c cell be- 

 comes transparent by losing its granular contents; the nucleus 

 then rounds off and comes to stain a darker color; finall}^, there 

 appear mitochondrial filaments around the nucleus. The cells 

 thus formed, yet containing neither zymogen granules nor large 

 nucleoli, remain for some time in the peripheral part of the islet, 

 during which period they store up, on the one hand, the nucleolar 

 substance so that the nucleolus increases in volume, and produce, 

 on the other, mitochondrial filaments which afterward can take 

 part in the formation of zymogen granules, as do the typical 

 acinus cells. 



Formation and fate of the typical islet 



From the above observations it follows that a cells are derived 

 from granular cells and that c cells are transformed into acinus 

 cells. On the other hand, there exist transitions between the 

 various types of islet cells; that is to say, between a cells and h 

 or e cells and between h and c cells. Considering the existence 

 of these transitions, it is conceivable that the cells constituting 

 the typical islet are supplied from acinus cells on the one hand, 

 and transformed into them on the other. The formation of the 

 typical islet (see text-figures) must be regarded as being inaug- 

 urated with the development of solitary a cells interspersed among 

 acinus cells from which they are derived (fig. 2 and text fig. a). 

 These solitary islet cells with the addition of a few newly formed 

 ones constitute small islets. They consist, for the most part, of 

 h cells, situated at the periphery, and of e cells, placed in the 

 center, the cells belonging either to an acinus or to two or 

 three neighboring acini (fig. 3). The latter is especially the case 

 if the islet shows a tendency to enlarge. But it cannot be said 

 that all of the small islets pass into the large typical ones. Most 



