THE SPLENO-PANCREATIC INTERNAL SECRETION. 403 



structures composed of dilated and tortuous capillaries." Opie 

 calls them "vascular islets" which are in "very free commu- 

 nication with the smallest arteries and apparently have a 

 richer blood-supply than other parts of the lobule." That 

 these dilated arteries are possessed of special functions is sug- 

 gested by the fact that, "if, instead of a solution of Berlin blue, 

 a granular injection mass for example, cinnabar or ultra- 

 marine blue is used, the islands may be injected, while the 

 intra-acinar capillaries contain little of the injected material." 

 They appear to constitute alveoli or ampullae rather than true 

 vascular channels, in which what blood passes through them is 

 submitted to some kind of process. 



An interesting feature in this connection was noted by 

 Opie, viz.: the fact that the cells of the islands of Langerhans 

 are in some instances continuous with the regular glandular 

 elements of the organ, in such a manner as to prolong the 

 ducts of the latter by encircling them. "Occasionally," says 

 the author, "one sees, apparently within the islands, cells ar- 

 ranged, as in the acini, about a central lumen, and, indeed, 

 in many instances, it is difficult to convince one's self that they 

 do not form part of it." This intimate relationship between 

 the two sets of glandular elements is further emphasized by 

 the manner in which their capillaries are related. While the 

 smaller arteries or arterioles ramify between the lobules and 

 supply the net-work of capillaries to the acini, they also com- 

 municate with the tortuous and dilated vessels of the islands 

 of Langerhans; so that the latter, as regards their vascular 

 relations, really constitute glomerular expansions and offshoots 

 of the regular acini's blood-channels. We thus have two sets 

 of superposed glands around a common duct, the upper, or 

 common acini, pouring their own secretion (or granules) into it 

 through their microscopical ducts; the lower, those of the 

 islands possessed of no ducts or other orifices presenting 

 their dilated capillaries or alveolar walls so as to cause them 

 to face, and perhaps slightly project into its lumen. If we 

 now replace by an active circulation through all these vessels 

 the cinnabar or ultramarine-blue injections referred to above, 

 the accumulation of the latter in the islands distinctly points 

 to a similar process during life: i.e., accumulation of blood and 



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