THE SPLENO-PANCREATIC INTERNAL SECRETION. 397 



dividing septa being incomplete. That these polygonal struct- 

 ures are actually independent of one another and represent 

 units of structure is readily demonstrated by causing an in- 

 flammatory increase of the interstitial tissue. If the pancreatic 

 ducts of a cat are ligated and the animal killed at the end of 

 two or three weeks, the gland is found to be the seat of a 

 chronic interstitial inflammation, characterized by an increase 

 of the interlobular tissue. The lobules are completely sepa- 

 rated from one another by narrow bands of firm, fibrous tissue, 

 and occur in sections as rounded, triangular, or polygonal 

 areas of parenchyma. 



"The islands of Langerhans occupy a position near the 

 center of the lobule, and in the splenic end of the gland each 

 lobule contains an island. In a given section many lobules 

 whose limits are more or less distinctly outlined are seen to 

 contain islands situated near their center, while in neighbor- 

 ing lobules such structures may not be discoverable. If, how- 

 ever, serial sections are studied, every lobule is found to con- 

 tain an island. Its presence within the lobule is not constant 

 in other parts of the organ, and in the extremity of the de- 

 scending arm of the gland they are very few in number. 



"The lobules are grouped about the medium-sized ducts. 

 The main ducts give off branches approximately at right angles 

 to their course. Branching one or more times, a duct forms 

 the center of a group of lobules, which is usually elongated in 

 form and tapers to a point at or near* the surface of the gland. 

 Such lobule groups are separated from one another by rela- 

 tively wide bands of areolar tissue much looser in texture than 

 that separating the individual lobules. The lobule groups in 

 the fresh state or in tissue macerated a few days in Muller's 

 fluid may be separated from one another by careful teasing. 

 In the loose tissue lie the larger ducts, arteries, veins, and 

 nerves. An artery and vein penetrate each lobule group in 

 company with the duct, and ramify between its lobules. The 

 smallest arteries occasionally penetrate the lobules, but usu- 

 ally branches, diminishing in size, give off capillaries which 

 enter the lobule and form a close net-work between the gland- 

 acini. 



"The capillaries of the island of Langerhans form a 



