218 Morphology alod Physiology of Areas of Langerhans
vascular network of the islands is made up of the windings,
branchings, and anastomoses of several larger vessels of venous
origin and large numbers of capillaries, which communicate inti-
mately with the interaciriar capillary plexus. The largest sinu-
soids are found in the central part of the islands, where the cords
of cells are relatively small. The periphery of the areas is gen-
erally much less vascular. The largest areas found in my series
were those of the rat, those of the guinea-pig being second.
The reconstructions show that the cords of cells have the exter-
nal form of branching and anastomosing tubules with occasional
alveolus-like enlargements; they are, however, solid structures
with no lumen and no arrangement of the cells and nuclei which
would suggest a lumen.
' The areas are generally larger and more numerous in the
central portion of the pancreas, especially in the bird, guinea-
pig, and rat. In most species, the islands are intimately related
to the glandular tissue, the capsule, when present, being so thin
and delicate that it is demonstrated with difficulty. In the new-
born child, however, most of the areas lie in the interlobular
connective tissue and are surrounded by it; in the guinea-pig,
the largest areas are in the connective tissue surrounding the
larger ducts and are independent or practically independent of
the pancreatic acini; and in some species of fish certain of the
islands are very large, constant in location, and entirely indepen-
dent of pancreatic tissue. In the human accessory pancreas,
islands may or may not be present, the number reported in which
they were absent being approximately equal to. that in which
they were present.
It is very natural to inquire concerning the function and mean-
ing of an organ so constant in its presence and structure at all
ages and in all species, occurring so early in embryonic life, and
maintaining its vitality with so few changes through all conditions,
and it is this side of the question which has interested the great
majority of the investigators of the islands of Langerhans. The
most varied views prevail. The discoverer, Langerhans, sug-
gested the possibility of a relation to the nervous system, since
these structures are often foind in close proximity to the sym-