Lyclia M. Dewitt 209
to get in sections a very good idea of the arrangement of the sinusoids and cap-
illaries in the islands. In Plate XIII, Figs. 3, 4, 5, and 6, are reproduced
models reconstructed from thin sections of these injected areas, the blood-
vessels only being used in the reconstruction. Three main types of arrange-
ment of vessels may be noted -(r) The vessel runs along the side, either
outside or just within the margin, of the area and sends branches mainly
from one side into the area; the branches cross the area, branching and
winding through it in every direction, and being often connected by anasto-
mosing capillaries. (2) One or two main branches pass through thc center
sending branches in every direction. (3) The main branch reaches thc center
of the area and there breaks up into branches which radiate in every direction.
In the models, the arrangement can be qluite easily traced in the smaller
islands of Langerhans, but in thc larger, the arrangement bccomes so com-
plicated that tracing is difficult, and the figure can givc only a very incormplete
idea of the arrangement. In the small islands, there is usually onc main (prob-
ably afferent) vein, which passes to one of the larger veins, either intcrlob-
ular or intralobular. Plate XIII, Fig. 3, shows a small and simplc area in which
thc arrangement of the blood-vessels may bc easily traced. A rclatively large
vein runs along thc side of the island and sends off a short principal afferent
vein. This breaks up almost at once into four smaller vessels, three of which
may be seen in the figure. After winding through thc area and branching and
anastomosing several times, fivc vessels leave the arca, two being capillary
in size and the others larger. In Plate XIII, Fig. 4, the main afferent
vessel divides, soon after entering the island, into five main branches
which branch and anastomose many times, the blood leaving the area by one
large efferent vein and six capillaries. The island represented in Plate XIII, Fig.
5, is composed of a plexus consisting of the branchings alid anastomoses of tvwo
larger vessels and twelve capillaries, while the still larger area represented in
Plate XIII, Fig. 6, shows a plexus composed of four larger vessels and fiftcen
capillaries with their branches. Two ot the large vesscls form an S-shaped
curve and again meet to form the core of the arca, the other branches and
capillaries twisting around and between them to makc up thc intricatc vas-
cular p]exus seen in the figure.
The hluman areas of Langerhans seem much more variable in structure than
those found in the other species studied, age and the gencral condition of the body
being more important factors in their structure than appears to be the casc in
most of the other vertebrates. This is especially true as concerns the insular con-
nective tissue. I have counted and measured areas of Langerhans (r) from a
four-year-old child (possibly syphi!itic), (2) from a newv-born, normal, healthy
infant, and (3) fron an apparently normal human adult. The measurements are
as followvs:
I II
I. .21 x .22 X .28 mm. .o 29 c. . x 7 x 3 mm 0033 .m.
2. .20 X .28 X .35 mm..oI96 c. mm. 20 x .21 x . I8 mm. .0076 c. mm.
3. .23 X .26 X .30 mm. .oI79 c.mm. .I6x .I8x .2omm. .oo58c.mm.
4. .I6 x .25 X .20 mm. .00o8 c.mm. .I5 X .î X I7 mm. .s38 c.mm
5. .I5 X .17 X .23 mm. .0059 c. mm. .I4x .15 x .I8 mm. .0037 c. mm.
6. .23 x .28 x .42 mm. .027 C. mm. .I3 x . 5 X . I4 Inm. .002o7 c. mm.