CYTOLOGICAL STUDIES OF LANGERHANS's ISLETS 37 



acinus cells, as seen in figure 7 (also text fig. b) . In the course of 

 time, this arrangement changes; the cells become elongated so 

 that there is interdigitation between the opposite cells (text fig. 

 c) ; the process continues until the upper ends of the cells touch 

 the basal membrane of the opposite side. Thus the typical cell- 

 cord of the islet is formed (text fig. d, and fig. 1). From this 

 mode of formation, it is evident that the diameter of the cord is 

 nearly the same as that of the acinus, most of the islet cell being 

 double the length of the acinus cell. The typical islet thus 

 formed seems to be in existence for a relatively long period, dur- 

 ing which the islet cells are formed by the conversion of acinus 

 cells, while some of them revert to the latter. This influences 

 not only the form, but also the size of the islet, and conditions 

 the inconstancy of the contour. From these circumstances, it is 

 conceivable that, if the newly formed islet cells exceed in number 

 those cells which are destined to return to the acinus tissue, the 

 islet would increase in size; and that, if the reverse is the case, 

 it would be reduced. In addition, the increase in volume of the 

 islet seems, in part at least, to be effected by the mitosis and 

 amitosis taking place within it; the decrease in volume, on the 

 contrary, is due entirely to the return of the islet cells to the aci- 

 nus tissue. Notwithstanding close inspection, I have not been 

 able to detect any degenerative process in islet cells, the ami- 

 totic figure often found in the islet being no sign of cell degen- 

 eration as shown in the previous chapter, 



I cannot say how long the typical islet exists as such. The 

 process of increase and decrease in bulk must take place very 

 slowly. It is also an extremely difficult matter to determine 

 whether an islet is in the course of development or of involution. 

 Laguesse ('01, '09-' 10) distinguishes between three periods in his 

 evolutionary cycle of the islet: the deconstitution period of the 

 acinus, the resting period, and the involution period of the islet. 

 I am of a different opinion, so far as I have been able to ascer- 

 tain, no such distinction can be made in the structure of vari- 

 ous islets, but one islet may contain cells in all three periods; in 

 other words, it may have not only b and e cells, but also a and c 

 cells. The ratio of these types of cells in the islet is not in every 



