410 Cytology of the Areas of Langerhans 
The adherents of one of these theories have consistently held that the 
islets produce a substance which, in one or another way, controls carbo- 
hydrate metabolism. This view, so carefully considered and so capably 
studied by Opie (14) has a particular significance when looked at in 
the light of my own experiments on the chemism of the islets, especially 
as regards the precipitability of the substances produced by the two 
types of cells mentioned above. What may be called the “ sugar function ” 
of the islets broadly suggests the outright physiological independence of 
the islets, and sharply marks off this view from that of the other party, 
the adherents of which have long urged the probability that the islets 
are merely exhausted acini which, as such, have no active function what- 
soever, but are, so to speak, in a state of rest, or obscuration, and, at the 
end of the cycle, return to the active state as typical pancreatic acini. 
These being the two main interpretations of the islets, a demonstration 
that the cells of the islets have a chemical value of their own (and are 
not, as a matter of fact, merely exhausted pancreas cells, but cells which, 
whatever may have been their former state, have, as islet cells, a positive 
function) would seem to be indirectly confirmatory of the sugar theory, 
or confirmatory at least of the broader notion that the islets have an 
independent physiological activity of their own. Such confirmatory 
evidence, I believe, will be found in the various chemical tests described 
below. 
A few words of history, bearing particularly on these considerations, are 
necessary here. For a larger historical review the reader is referred to 
Oppel (13) and to Sauerbeck (19). The latter has an ample review of the 
pathological as well as of the anatomical literature of the islets. 
The structures called the Islets of Langerhans were discovered by 
Langerhans (10), who first called attention to them in 1869. The same 
year (subsequently to Langerhans’s announcement) the name ‘ Les ildts 
de Langerhans’ was applied to them by Laguesse. Kiihne and Lea 
afterwards gave them the name of “intertubular cell clumps.” They 
have been called secondary cell groups (by Harris and Gow), points 
folliculaires (by Renaut), and Islands of Langerhans (by American 
anatomists) . 
The history of the islets from the date of their discovery until 1886 
is chiefly interesting for the controversies it contains, and for the opinions 
hazarded as to the nature and function of the structures. Langerhans 
himself believed them to be the end-apparatus of nerve fibers. Renaut 
(17) described them in a very general way, and was unfortunate in being 
misquoted by some earlier writer who, since Renaut’s announcement 
in 1879, has been extensively followed throughout the whole of the 
