CYTOLOGICAL STUDIES OF LANGERHANS's ISLETS 3 



belonging to different tissues are in close apposition, although a 

 transition between them is not conceivable. 



Those who have tried to solve this problem experimentally have 

 hgatured the pancreatic duct, allowed the animal to fast, or in- 

 jected pilocarpi!! or secretin, and studied the changes thus pro- 

 duced in the size and number of the islets. Their observations 

 have not, however, been in accord. Some (Fischer, Dale, and 

 Vincent and Thompson) believed that they found an increase in 

 the number of islets in starvation, while others noticed neither 

 an increase nor a decrease of the islet tissue. On the other hand, 

 ligature of the pancreatic duct caused, in some instances, the dis- 

 appearance of only the acinus tissue, the islet remaining intact; 

 in others, the disintegration of both tissues. That lack of uni- 

 formity in the results of these experimental investigations is 

 perhaps due primarily to an inequality in the experimental 

 methods employed; secondly, to the fact that the islets vary 

 greatly in size and number not only in the different animals, but 

 also in different portions of the same pancreas, as has been 

 pointed out by various investigators. Under these circumstances 

 there is always a danger of misinterpretation when one attempts 

 to draw any general conclusion from the changes in size and num- 

 ber of islets in any circumscribed area of the pancreas. 



It will be seen from the foregoing that the evidence brought 

 forward to show a transition between the islet and the acinus tis- 

 sue is by no means positive. The points which morphologists 

 must solve first of all are: ''What are islet cells? What is their 

 internal structure or specific property? The characteristics of 

 islet cells pointed out by various investigators are not an accurate 

 index. It has been claimed that these cells are distinguished 

 from acinus cells in the following details: 1) they contain no 

 zymogen granules and therefore appear more transparent; 2) 

 they form groups showing a definite disposition; 3) a lumen in 

 continuity with the pancreatic duct cannot be discovered within 

 the islet; 4) the form, structure, and staining reactions of the 

 nuclei of islet cells are different from those of acinus cells; 5) some 

 islet cells contain a certain type of granules. Of the above, 1 

 and 3 are not characteristic of islet cells alone; there are, on the 



