420 Cytology of the Areas of Langerhans 
transforming themselves into the cells of the islets which I consider 
improbable, that transformation must be regarded as a physiological as 
well as a morphological one. In the course of an examination of many 
hundreds of islets in the pancreas of the guinea pig I have been able to 
find but one example of what might be interpreted as a vestige of a 
lumen ; and this singular structure seemed to be formed by cells of the A 
type. 
There is one remaining aspect of the problem to be touched upon 
before closing. This is the possibility that the A and the B types of cell 
are in reality two different phases of the same cell—a notion by no means 
improbable even in the face of the chemical evidence to the contrary. 
Professor Bensley, who has examined my preparations with considerable 
care, has pointed out cells which seem (from the anatomical side) to be 
intermediate between the two types, especially in certain preparations 
which, at his suggestion, were treated with Ehrlich’s hematoxylin before 
they were submitted to the neutral gentian bath. But even granting the 
truth of this observation, the force of the general argument remains. If 
the A and £ cells are really phases of one and the same cellular structure, 
their different chemical characters suggest that they are engaged in the 
manufacture of two different secretions. If we conceive that the A cell 
changes into the B cell, or vice versa, we must conclude that the change 
implies the taking on of a different physiological activity. Whether or not 
these two different secretions have to do with the pancreas itself or, 
through the pancreas with functions lying, in their special or general 
effects upon the chemistry of the body, near to or remote from, the 
pancreas, is a matter to be determined by further research. 
I have to thank Professor Bensley, who was kind enough to direct my 
researches, for his lively interest in the work, for his invaluable sugges- 
tions as to technique, for his assistance in the interpretation of difficult 
nodi that arose as the work developed, and for having made preliminary 
reports of the work to the Association of American Anatomists. My 
thanks are also due to Mr. Leonard H. Wilder for the fidelity of the 
drawings which accompany this paper. 
LITERATURE. 
1. Benstey, R. R.—The @sophageal Glands of Urodela. Biological Bulletin, 
Wood’s Holl, Vol. II, pp. 87-104, 1906. 
2. Date, H. H.—On the Islets of Langerhans in the Pancreas. Phil. Tr.; 
Lond., CXCVII, Bd., pp. 25-46, 1905. 
3. DeWitt, L. M.—Morphology and Physiology of Areas of Langerhans in 
Some Vertebrates. Jour. of Exp. Med., New York, Vol. VIII, pp. 
193-239, 1906. 
