602 PHYSIOLOGY 



some zymogen granules. One may conclude that the islets of 

 Langerhans represent, not a tissue sui generis, but a stage in the 

 life history of the secreting cells of the pancreas. Whether they 

 subsequently build up basophile material and from this new granules, 

 or whether they are cleared away to be replaced by newly formed 

 tissue, we do not know. The fact, however, that in the embryo a large 

 amount of the pancreas is of the nature of islet tissue suggests that 

 the islets and exhausted cells found in a thoroughly exhausted gland 

 may later on undergo regeneration and be re-formed into secreting 

 cells. 



This conclusion may have to be revised in the light of more recent researches, 

 especially by Bensley. It seems to be generally agreed that the islets may be 

 formed throughout life by growth from the ducts of the glands. By appropriate 

 methods they may be shown to contain fine granules, differing altogether in 

 staining reactions from the zymogen granules of the secreting acini. According 

 to Bensley, neither the number nor the situation of the specifically stained islets 

 undergoes any change as a result of starvation or of exhaustion of the gland. It 

 must be acknowledged that Dale's criteria of islet tissue were chiefly negative, 

 and that unless the sections be treated so as to display the specific granulation 

 of the islet tissue, it would not be possible to distinguish it from completely 

 exhausted secreting cells, which had lost their basophile substance as well as 

 their zymogen granules. The question cannot be regarded as finally decided. 



