THE CYTOLOGICAL CHARACTERS OF THE AREAS OF 
LANGERHANS. 
BY 
M. A. LANE. 
From Hull Laboratory of Anatomy, University of Chicago. 
WITH 1 PLATE. 
In the course of a comparative study of the pancreas, begun in the 
autumn of 1905, I was struck with a peculiar reaction in certain cells of 
the Islets of Langerhans in the pancreas of the guinea pig—one of the 
first animals used in the study. This reaction,—to be described presently, 
—indicated the existence in the islets of two types of cells, chemically 
and morphologically different from each other. A part of the ensuing 
investigation is the subject of the present paper, which is to be followed 
by a further publication dealing in detail with a comparative study of the 
islets which I have carried on side by side with that of the islets in the 
guinea pig. 
The principal difficulty thus far in dealing with the Islets of Langer- 
hans has been the want of a definite method by which to distinguish the 
cells of the islets from the cells of the pancreas itself; for although there 
is an apparently constant content of islet tissue in the pancreas, and 
although the areas of islet tissue, in sectioned pancreas, stand out in sharp 
contrast with the tubules of the pancreas, the physiological distinctness 
of the one kind of tissue from the other is the very question upon which 
histologists and pathologists have most disagreed. Pancreas cells ex- 
hausted by stimulation with alkaloids, and thus thoroughly discharged 
of their secretion products, have thus far been indistinguishable—so far 
as positive evidence goes—from cells of the islets; so that it has been 
impossible to say that exhausted cells which are indisputably pancreas 
cells are not essentially the same as islet cells; and, on the other hand, 
that cells which are indisputably islet cells are not in reality exhausted 
cells of the pancreas. To establish a method of differentiation between 
these two orders of cells was a purpose which thrust itself forward very 
early in the work, as the establishment of such a method would go far 
toward testing the claims of the two leading theories respecting the 
meaning of the islets. 
AMERICAN JOURNAL OF ANATOMY.—VOL. VII. 
32 
