Lydia M. Dewitt 203
which only the small capillaries and the few afferent and efferent vessels pass.
In the rat, however, the cells at the periphery are to some extent arranged
in irregular cylinders resembling tubules in contour, but having no lumen and
having a very free communication with other cylinders. The cells of the rat's
insulæ are very similar to those already described for the guinea-pig. Large col-
umnar cells with large nuclei arranged in definite bands consisting of one to
two rows of cells occupy the central portion, while at the periphery most of the
cells are smaller, the nuclei more crowded and the arrangement less band-like;
the blood-vessels are smaller andless prominent. Fig. 3 represents the appear-
ance of a section through the central part of a small area of Langerhans from the
rat's pancreas.
Fig. 3.-Section through central part of area of Langerhans from pancreas of
rat. X 200.
In this series of sections, there was passive congestion, so that
all veins and venous connections were filled with blood, while
the arteries were as a rule empty. It was therefore an especially
favorable series of sections for determining the relation of the
vascular supply to the pancreatic vessels. As stated before,