STUDIES ON THE PANCREAS OF THE GUINEA PIG 347 



geneous, unless it contains a secretion antecedent, in which case 

 the portion of the cell along the lumen contains irregular granules 

 which stain with mucicarmine. A few goblet cells may be pres- 

 ent among the epithelial cells, though rarely are these found. 

 At irregular intervals small flask-shaped mucous glands open 

 into the tubules. The lumen of the tubules is continuous through- 

 out, though, in places, it may be as narrow as 1.5 micra. 



When stained in neutral red as well as pyronin, and studied 

 under the oil immersion, some of the projections on the tubules 

 are seen to be composed of cells which stain like islet cells, al- 

 though some of these cells contain fewer granules than the typical 

 islet cell. Single islet cells may also be seen here and there among 

 the epithelial cells of the tubules. In addition to these islet ele- 

 ments, islets of every conceivable size, from the smallest to the 

 largest in the pancreas, are attached to these tubules, either 

 directly, in which case the islet is a rounded projection on the side 

 of the tubule, or indirectly, when the islet is connected with the 

 tubule by a longer or shorter stalk which is of the same nature 

 as the tubules from which it springs. 



Also attached to these tubules, but less frequently than the 

 islets, are small pancreatic lobules, varying in size from a single 

 acinus to a group of acini. In some cases these acini arise from 

 the ducts which lead to the islets. In these acini, and in the small 

 islets which are attached to the tubules, as well as in the tubules 

 themselves, occasional mitoses may be observed, though these are 

 rare except under those conditions where there is defect of pan- 

 creatic tissue as the result of removal of a portion of the pancreas, 

 or in young animals in which the pancreas is rapidly growing. 



The single islet cells which are to be found among the epithelium 

 of these tubules may be interpreted as cells which have been dif- 

 ferentiated out of the epithelium of the tubules, and similarly the 

 regular gradations in size of the islets of this system, from the 

 smallest to the largest, as well as the presence of small lobules of 

 pancreatic acini attached to the tubules, together with the oc- 

 currence of mitoses in all the anatomical elements of this group, 

 indicate that we have to do here with a tissue of a low order of 

 differentiation, which is capable under proper conditions, of 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 12, NO. 3 



