M. A. Lane 419 
SUMMARY AND CONCLUSIONS. 
Recapitulating the facts above described the following positive state- 
ments may be made: 
1. In the Islets of Langerhans in the guinea pig’s pancreas two types 
of cells, morphologically and physiologically distinct, are demonstrable. 
These cells show constant reactions to constant chemical tests. I have 
called these cells A and £ cells, respectively. 
2. The granular content of the A cell differs chemically from that of 
the B cell. 
3. The granular contents of the A cell and of the 6 cell, while differing 
chemically from each other, differ chemically from the granular content 
of the pancreas cell, and cannot, therefore, be identical with zymogen. 
4. The granular contents of the A and of the @ cell differ chemically 
from the prozymogen manufactured by the pancreas cell as the antecedent 
of the zymogen granule of the pancreas cell. 
5. The chemical and morphological differences between the A and the B 
cell are correlated; that is, the relations between the anatomical and 
physiological characters of both types are found to be constant. 
In drawing conclusions from these facts one is led to the conviction that 
the Islets of Langerhans are structures which in all probability have the 
function of producing a twofold substance which, poured into the blood 
stream, has an important effect upon metabolism. That this dual 
character of cell in the islet is constant throughout the entire class of 
mammals, if not throughout the entire phylum of vertebrates, is indicated 
as probable from the results of the comparative study now in progress, 
which I hope to make the subject of a future publication. The prospects 
seem to point to certain peculiar variations in the character of these cells 
in herbivora and carnivora, and to striking and highly suggestive varia- 
tions among herbivora themselves. 
While these results do not prove that pancreatic cells do not transform 
into islet cells, or vice versa, they furnish very strong reasons for holding 
that under normal conditions the islets are physiologically independent 
of the rest of the pancreas—a conclusion in accord with the observations 
of De Witt and Flint as to the framework and architecture of these 
structures, and with those of Opie, Pearce, and Helly as to the early 
differentiation in the embryo of the specific cells which are their histo- 
genetic source. 
It is but rational to conclude from the chemical evidence that the 
substances produced by the two types of cells of the islets are not to be 
classified with zymogen. If the cells of the pancreas have the power of 
