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494 DIGESTION.
parts of the intestine, which are chiefly, if not entirely, to be considered
as absorption organs. The investigations on the action of this secretion
on nutritive bodies have not as yet yielded any positive results.
IV. THE PANCREAS AND PANCREATIC JUICE.
In invertebrates, which have no pepsin digestion and which also
have no formation of bile, the pancreas, or at least an analogous organ,
seems to be the essential digestive gland. On the contrary, an anatom-
ically characteristic pancreas is absent in certain vertebrates and in
certain fishes. Those functions which should be regulated by this organ
seem to be performed in these animals by the liver, which may be
rightly called the hepatopancreas. In man and in most vertebrates
the formation of bile, and of certain secretions, containing enzymes
important for digestion, is divided between the two organs, the liver and
the pancreas.
The pancreatic gland is similar in certain respects to the parotid
gland. The secreting elements of the former consist of nucleated cells
whose basis forms a mass rich in proteins, which expands in water and
in which two distinct zones exist. The outer zone is more homogene-
ous, the inner cloudy, due to a quantity of granules. The nucleus lies
about midway between the two zones, but this position may change
with the varying relative size of the two zones. According to Heiden-
hain * the inner part of the cells diminishes in size during the first stages
of digestion, in which the secretion is active, while at the same time
the outer zone enlarges owing to the absorption of new material. In
the later stage, when the secretion has decreased and the absorption
of the nutritive bodies has taken place, the inner zone enlarges at the
•expense of the outer, the substance of the latter having been converted
into that of the former. Under physiological conditions the glandular
cells are undergoing a constant change, at one time consuming from the
inner part and at another time growing from the outer part. The
inner granular zone is converted into the secretion, and the outer, more
homogeneous zone, which contains the repairing material, is then con-
verted into the granular substance. The so-called islands of Langer-
hans are related to the internal secretion or contain a substance taking
part in the transformation of the sugar of the animal body.2
The chief portion of protein substances contained in the gland con-
sists, it seems, of a protein insoluble in water or neutral salt solution and
1 Pfluger’s Arch., 10.
1
See Diamare and Kuliabko, Centralbl. f. Physiol., 18 and 19; Rennie, ibid., 18;
Sauerbeck, Yirchow’s Arch., 177, Suppl.
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