STUDIES ON THE PANCREAS OF THE GUINEA PIG 311 



THE NUMBER OF ISLETS OF LANGERHANS IN THE PANCREAS OF 



THE GUINEA PIG 



The determinations of the number of islets in the pancreas of 

 the guinea pig have been made by means of the neutral red vital 

 staining method described under technique. Some idea of the 

 character of the preparations in which the islets were counted 

 may be obtained from figs. 1, 2, and 3, which are reproductions 

 of photographs made from preparations of the pancreas of the 

 guinea pig, stained by injection with neutral red and mounted 

 without teasing and with but slight pressure under a cover glass. 

 All three were made from the same preparation, and so give an 

 idea not only of the large proportion of islet tissue in the pancreas, 

 but also of the variation of this proportion within narrow limits 

 of space. As the figures indicate, every islet from the smallest 

 to the largest stands out clearly stained in the preparations. The 

 largest islet shown in these figures measures 0.5 mm. in diameter, 

 while the smallest measures 50 micra. These are not, however, 

 the limits of size in the guinea pig, for the smallest islet is a single 

 islet cell included among the cells of a ductule or among the zymo- 

 genic cells of an acinus, while occasionally, as Dewitt ('06) has 

 pointed out, one may find islets having a diameter of 1 mm. Such 

 single islet cells are, however, comparatively rare in the guinea 

 pig after the first two weeks of life, although in individual cases 

 they may present in considerable number among the epithelial 

 cells of certain branches of the duct system which will be described 

 later. 



To secure a resting condition of the pancreas the animals were 

 kept without food for twenty-four hours and, in addition, each 

 animal at intervals of twelve hours was given hypodermically 

 two doses of one- twentieth to one-tenth of a grain of atropine 

 sulphate. By this means secretion is checked and the pancreas 

 is permitted to store up zymogen. I did not consider it wise to 

 prolong the period of fasting beyond this limit because of the 

 claim of Dale ('05) and of Vincent and Thompson ('07) that fast- 

 ing as well as active secretion increases the number of islets. At 

 first I hoped that, when the whole pancreas was considered, the 

 variation in number of the islets would not be great, even though 



