204 fMorphology and Physiology of Areas of Langerhans
v. Ebner and Diamare regarded the vessels of the areas as venous,
while Laguesse, Opie, KUhne and Lea, Pensa and others believed
it to be arterial, and Hansemann finds only capillary connections.
After a most careful investigation of this series of sections as
well as of many others from this and many other species, I have
never been able to demonstrate an arterial connection with the
vessels of the areas, since I have not found a vessel with distinct
muscular coat either entering the areas or sending branches
into them. Sometimes an arteriole was seen apparently ap-
proaching an area, but on tracing it through the series of sections,
it was seen to turn aside or pass over the area without communi-
cating with it. In cases of venous congestion, the blood-vessels
of the islands are always packed with blood, and in a few cases,
as in Fig. 4, I have been able to trace the main vessel, which
have regarded as afferent, directly to a vein, beside which ran
an artery with distinct muscular coat. In double injections, as
will be shown later, it is always the venous injection mass which
fills the blood-vessels of the areas. I have therefore regarded
the blood-vessels of the areas as venous with abundant capillary
connections with the surrounding interacinar capillary plexus.
Nearly always in tracing areas through a series of sections, at
least one and sometimes more than one larger vein, usually aris-
ing either from an interlobular or intralobular vein, has been seen
to enter the area and this I have designated as the principai
or afferent vein, while several smaller venules and large numbers
of capillaries leave the area in all directions. Since all of these
vessels have the same structure, it is difficult, except by the
size, to determine which are afferent and which efferent, and
we can say only that several larger veins and numerous
capillaries form a rich plexus of large, irregular, thin-walled
blood-vessels, which, in accordance with Minot's characterization,
I regard as sinusoids. The insular vessels always have a different
arrangement from that of the interacinar vessels, but the arrange-
ment is variable, especially in sections. Since the areas of the
rat are usually much longer than they are wide, the principal
vessel usually enters at the side, often passing, as in Fig. 4, to
near the center of the island and there breaking up into branches,