THE PANCREAS. 



1735 



FIG. 1463. 



Alveolus 



are usually of a blunted pyramidal shape, although many aberrant forms are seen, 

 with an average length of about .010 mm. During functional inactivity their cyto- 

 plasm exhibits two well-differentiated zones : an inner one, next the lumen, which is 

 highly granular, and an outer one, next the basement membrane, which is free from 

 granules and at times almost homogeneous. The round or oval nucleus occupies 

 the external area. The relative breadth of these two zones varies with the func- 

 tional activity of the cells. During fasting, when the latter are stored with zymogen 

 particles, the granular zone is very broad and the outer homogeneous one corre- 

 spondingly narrow. With beginning discharge of the pancreatic secretion during 

 digestion, the granular zone diminishes and reaches its minimum, almost dis- 

 appearing when the gland is exhausted. The return of the latter to a condition of 

 rest is accompanied by the formation and gradual accumulation of a new store of 

 zymogen particles until the granular zone is again restored to its maximum. Occa- 

 sionally in fixed tissue the parietal cells exhibit within their cytoplasm a body 

 termed t\\o. paranucletis (Nebenkern). The latter is of uncertain form, often singu- 

 larly round and indented, and 

 smaller than the nucleus in the 

 vicinity of which it usually lies. 

 The nature and significance of 

 this body are still undeter- 

 mined, some observers regard- 

 ing it as a derivative from ex- 

 truded nuclear material, the 

 paranucleus, in turn, being con- 

 cerned in producing the zyrno- 

 gen-granules. Intercellular se- 

 cretion-capillaries have been 

 demonstrated in the alveoli of 

 the pancreas. They extend 

 between the cells for some dis- 

 tance, but do not reach the 

 basement membrane surround- 

 ing the acini. Intracellular 

 secretion-vacuoles are also de- 

 monstrable at times by means 

 of Golgi stains, but are tem- 

 porary and cannot be regarded 

 as constant details of the cells 

 (Ebner). 



The interalveolar cell- 

 areas, or islands of Langer- 

 hans, appear as small collec- 

 tions of cells, some .3 mm. in diameter, lying between the tubular acini, from which 

 they are separated by a delicate envelope of connective tissue. These cell-areas are 

 constant features of the pancreas, not only of man, but likewise of a wide range of 

 animals representing mammals, birds, reptiles, and amphibians. Their distribution 

 within the pancreas is by no means uniform, since, as has been shown by Opie, 1 while 

 about equally numerous in the head and adjacent part of the body of the organ, they 

 may be almost double in number towards the tail. The cells composing these masses, 

 although developed from the same tissue which gives rise to the usual glandular 

 elements of the pancreas, differ from the latter in being smaller, polygonal rather 

 than pyramidal in form, less granular, and undifferentiated into the characteristic 

 zones usually seen in the pancreatic cells. They are arranged as a net-work con- 

 sisting of solid cords or trabeculae, the meshes of which are occupied by blood- 

 capillaries of large size ; the whole recalling the arrangement of hepatic tissue. No 

 extension of the system of excretory tubes has been demonstrated within these 

 cell-islands, secretion-capillaries being therefore wanting. The significance of the 

 islands of Langerhans has long been a subject of dispute, but in view of their isola- 



1 Johns Hopkins Hospital Bulletin, September, 1900. 



Interlobular 

 5^ duct 



Interlobular 

 blood- 

 vessels and 

 nerve 



Section of pancreas, showing interlobular connective tissue with vessels 

 and duct surrounded by tubular alveoli. X 200. 



