446 The Islands of Langerhans in the Human Embryo 
has, I think, supplied convincing proof upon points which have hitherto 
been in much doubt, and it affords, in my opinion, a consistent and sat- 
isfactory explanation of the development of the islands. I have been 
able, in addition, to confirm the results of the study of their develop- 
ment in normal organs, with a study of the appearances which they pre- 
sent under the peculiar pathological changes which affect the pancreas in 
congenital syphilis. 
The work falls into two categories: (1) the study of the embryonic 
normal pancreas, and (2) the study of the pancreas in congenital syphilis. 
Of the second portion of the study, only those parts which confirm or 
aid in explaining the normal development will be presented at this time. 
For the materials for this study, I am indebted to Professor Marchand, 
of Leipzig, to Professor Mall, of Baltimore, and Dr. Longcope, of Phila- 
delphia, to whom I wish to express my sincere thanks. 
Review of the Literature——A comprehensive description of the de- 
velopment of the islands in the human embryo, I have not been able to 
find. Laguesse (1) in his description of the embryology of the pancreas 
of the sheep gives a very complete picture of the early development of the 
islands. At an early period, the end of the second month (embryo of 
18.5 to 50 mm.), the primitive gland structure of the pancreas, composed 
of solid cell masses, present here and there, generally along the outer 
border, cells which stain more darkly than th® general mass. These cells 
proliferate, lose their granular appearance, and fosm protruding loops or 
swellings, spheroid or ovoid in shape. They remain in connection with 
the tubules for some time and constitute the “primary islands” (clots 
endocrines). Later, in embryos of about 90 mm., these structures 
atrophy and are replaced by similar structures formed by proliferation 
of the fully formed secreting tubules of the acinus. These “secondary 
islands” eventually become tunnelled and vascularized. Laguesse at 
this time, 1897, believed that they were formed not only during em- 
bryonic life but throughout adult life and represented a portion of the 
gland temporarily modified for a special function, an internal secretion 
apparently essential to foetal life. He believed, also, that it was possi- 
ble for these modified structures to revert to the glandular type. Later 
(2), however, he modified this conception in that although he consid- 
ered this transformation possible, yet he believed that some of the islands 
persisted as such throughout life. This change of view was due to the 
work of Diamare (3) who, supported by Massari (4), insisted that the 
islands were definite, constant, and unchanging formations, formed early 
in embryonic life and persisting until death. Both of these writers 
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