. The endocrine organs; an introduction to the study of internal secretion . stherefore probably manifested directly upon the cells of the organ they stimulateand not through the nerve terminations. THE INTERNAL SECRETION OF THE PANCREAS. THE ISLETS OF LANGERHANS The pancreas contains, besides its alveoli and the ducts which conducttheir secretion into the duodenum, a peculiar epithelial tissue occurringin most animals in the form of small isolated masses interspersed through-out the gland, and known from their discoverer (1869) as the islets ofLangerhans (fig. 88). Although quite distinct in
. The endocrine organs; an introduction to the study of internal secretion . stherefore probably manifested directly upon the cells of the organ they stimulateand not through the nerve terminations. THE INTERNAL SECRETION OF THE PANCREAS. THE ISLETS OF LANGERHANS The pancreas contains, besides its alveoli and the ducts which conducttheir secretion into the duodenum, a peculiar epithelial tissue occurringin most animals in the form of small isolated masses interspersed through-out the gland, and known from their discoverer (1869) as the islets ofLangerhans (fig. 88). Although quite distinct in appearance and in thecharacters of their cells from the epithelium of the alveoli, the study oftheir development shows that they originally grew out from the buddingducts, and that their cells have therefore an origin in common with thoseof the alveoli. But they have no open communication with the ducts oralveoli. The number of islets in the pancreas is very variable, and thisvariability has led to inferences being drawn regarding their appearance 126 The Endocrine Organs. FIG. 88.—Section of pancreas of dog, showing an isletof Langerhans between the alveoli. Magnified 200diameters. and disappearance which in many cases are probably not justifiable. ThusBensley found a variation in the guinea-pig in animals of different ages of from 10 to 189 islets permilligramme of pancreas: inthe mature animal the varia-tion was from 10 to 25. Theenumerations of Clerk ledhim to the conclusion thatin the normal human pan-creas there may average 10to 20 islets in each milli-gramme of the gland, whichroughly would give aboutthree-quarters of a millionto a million and a half forthe whole pancreas. In Teleostean fishesRennie has shown that thereis one very large mass of islettissue which is encapsuled byconnective tissue and practi-cally forms a separate in other animals theislets are closely encircled by and in contact with the alveolar tissue, andsometimes appear to be continued int
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