PANCREAS 639 



ferment, or at least possess the power of destroying sugar. Yet the 

 question of the significance of the islets can hardly be 'considered 

 settled, although, as previously mentioned, the supposed experi- 

 mental basis of the theory that they do not differ essentially from 

 the alveolar tissue, but are formed by certain changes in the arrange- 

 ment and properties of the alveolar elements, appears to have 

 collapsed under the criticism of Bensley and others. Far from 

 being interchangeable with the cells of the acini, the islet cells 

 presr.nt definite and permanent criteria by which they can be sharply 

 distinguished from the alveolar epithelium. At least two types of 

 islet cells may be identified by their staining reactions, the so-called 

 A and B cells (Lane). The B cells are the most abundant in 

 all the islets, and many of the small islets are composed of them. 

 In the guinea-pig, on account of the great size of some of the islets, 

 and because many of them are situated in the interstitial tissue 

 (between the acini), it is not difficult to pick out an islet, isolate it 

 from the surrounding tissue, and examine it in serum or salt solu- 

 tion. The cells are crowded with very fine granules exhibiting 

 Brownian movement. In the fresh preparation the granules of the 

 A cells cannot be distinguished from those of the B cells. 

 Both varieties stain intensely with neutral red and other dyes, and 

 the islet tissue can in this way be easily differentiated from the 

 tissue of the acini. By differences in their staining reactions and 

 certain properties of their nuclei, which need not be gone into here, 

 the two varieties of islet cells can be identified. The important 

 point for our purpose is that by an appropriate histological tech- 

 nique the islet tissue can be studied in all the functional vicissitudes 

 of the gland. When this is properly done, it is not found that 

 there is any close connection between the secretory activity of the 

 cells of the acini and the islets. Nor is there any evidence that the 

 amount of islet tissue in the pancreas is ever affected by the forma- 

 tion of new islets out of acini. On the other hand, it seems that the 

 islets, or the great majority of them, consist of epithelial cells which 

 are in direct continuity with the pancreatic ducts, and that after 

 removal of a portion of the pancreas, establishing an insufficiency of 

 islet tissue, new islets can be developed from the duct epithelium, 

 in addition to the increase by interstitial growth in the size of islets 

 already existing (Bensley, etc.). If the islets are connected with 

 the ducts, the possibility may be admitted that they yield some- 

 thing to the external secretion of the pancreas as well as to its 

 internal secretion. But if this be so, there is no improbability in 

 the idea that the alveolar epithelium, which is undoubtedly mainly 

 concerned in the preparation of the pancreatic juice, may also 

 contribute something to the internal secretion of the gland. While, 

 then, the importance of the pancreas in carbo-hydrate metabolism 

 is certain, and the dependence of this function upon an internal 



