202 JIiorphology aotd Physiology of Areas of Langerhans
that of the surrounding acini, and the arrangement is so different
that the areas are sharply differentiated from the acini by the ar-
rangement of the connective tissue alone. Fig. 2 shows a section
through the center of a rather typical intralobular area of
Langerhans of the guinea-pig. It is surrounded by pancreatic tu-
bules except at one end, where the area reaches the periphery of the
lobule and is limited by the interlobular connective tissue. The
large columnar cells, single or double rows of which form the cen-
tral cords of the area, and the more crowded cell masses at the
periphery are well seen. These peripheral masses resemble some-
what the description given by Harris and Gow of the areas of
Langerhans of the guinea-pig,-masses of nuclei, not differenti-
ated into cells, and somewhat resembling lymphoid tissue-but
the area as a whole is distinctly different.
In the rat also, the areas near the center of the pancreas are larger and more
numerous than those near the periphery, but I have never, in the material at
hand, been able to find the large isolated or nearly isolated central areas so
characteristic for the guinea-pig. The measurements given below indicate to
some extent the variations in size and shape of the areas of Langerhans in the
I. 0.53 x 0.27 x 0.26 mm......0037 c. mm.
2. 0.50 x 0.43 x 0.32 mm ........ o.o0688 c. mm.
3. o.I4 x 0.38 x 0.22 mm........ o.oI8 c. mm.
4. 0.22 x o.23 x o.40 mm............o02 c. mm.
5. 0.26 x 0.62 x o .475 mm ...........o 076 c. mm.
6. o.I6 x 0.25 x 0.30 mm ......0..o12 c. mm.
7. 0.3o x 0.60 x o.5g mm.0..........092 C. mm
8. o. I4 x o.I8 x 0.29 mm...... .oo.0.007 c. mm.
9. o.I7 x 0.51 x o.465mm....... .o o4c. mm.
IO0. o.1 x o.I8 x 0.2I mm . ..................0.0376 c. mm.
The average size of these ten areas is . 0376 c. mm. and, as the average num-
ber is o. 7 per mm. in the material at hand, about T~ of the pancreas consists
of insular tissue. It is somewhat difficult to be sure of counting areas correctly
in the rat, since most of the areas are irregular and lobulated so that often areas
may appear as two quite widely separate areas in one section, while in another
they unite into one relatively large island. This can easily be seen from Plate
XII, Fig. I, which reproduces a model of a typical area of Langerhans from the
rat's pancreas. This island of Langerhans is not nearly so large nor so lobulated
as islands often appear, in tracing them through the series of sections in which
they occur. It consists of two distinct lobules of insular tissue, well separated
at the periphery, but joined at the center into a solid mass. The sponge-like
appearance of these areas is well seen in the figure, since, as stated before, the
relatively loose, band-like arrangement of the cells at the center is concealed
to some extent by the more solid masses of small cells at the periphery, through