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524 DIGESTION.
we often find in the large intestine, balls similar to the so-called hair-
balls (see below). Such calculi contain calcium and magnesium phos-
phate (about 70 per cent), oat-bran (15-18 per cent), soaps and fat (about
10 per cent). Concretions which contain very much fat (about 74 per
cent) occasionally occur, and those consisting of fibrin clots, sinews,
or pieces of meat incrusted with phosphates are also rare.
Intestinal calculi often occur in animals, especially in horses fed on bran.
These calculi, which attain a very large size, are hard and heavy (as much as 8
kilos) and consist in great part of concentric layers of ammonium-magnesium
phosphate. Another variety of concrements which occur in horses and cattle
consists of gray-colored, often very large, but relatively light stones which contain
plant residues and earthy phosphates. Stones of a third variety are sometimes
cylindrical, sometimes spherical, smooth, shining, brownish on the surface, con-
sisting of matted hairs and plant-fibers, and termed hair-balls. The so-called
" ^egagropil.e," which occur in the antilope rupicapra, belong to this group,
and are generally considered as nothing else than the hair-balls of cattle.
The so-called oriental bezoar-stone also belongs to the intestinal concrements,
and probably originates from the intestinal tract’ of the capra .egagrus and ante-
lope dorcas. There may exist two varieties of bezoar-stones. One is olive-
green, faintly shining and formed of concentric layers. On heating it melts with
the development of an aromatic odor. It contains as chief constituent lithofellic
acid, C20H36O4, which is related to cholic acid, and besides this a bile-acid, litho-
bilic acid. The others are nearly blackish brown or dark green, very glossy,
consisting of concentric layers, and do not melt on heating. They contain as
chief constituent ellagic acid, a derivative of gallic acid, of the formula CuHeOs,
which, according to Graebe, 1
is the dilactone of hexaoxydiphenyldicarboxylic
acid, and which gives a deep-blue color with an alcoholic solution of ferric chlo-
ride. The last-mentioned bezoar-stone originates, to all appearances, from the
food of the animal.
Ambergris is generally considered an intestinal concrement of the sperm whale.
Its chief constituent is ambrain, which is a non-nitrogenous substance perhaps
related to cholesterin. Ambrain is insoluble in water and is not changed by boil-
ing alkalies. It dissolves in alcohol, ether, and oils.
VI. ABSORPTION.
The contents of the intestine are gradually pushed onward by the
peristalsis or rhythmical movement of the intestinal musculature, but
the mechanism is not well known.2
By these processes the intestinal
contents are intimately mixed and the constituents of the food which
are valuable to the organism are transformed, in the manner previously
mentioned, so that they are adaptable for the processes of absorption.
In discussing the absorption processes we must treat of the form into
which the different foods are changed before absorption, of the man-
ner in which this is accomplished, and lastly, of the forces which act
in these processes.
1
Ber. d. d. chem. Gesellsch., 36.
2
See Cannon, Amer. Journ. of Physiol., 6, 12, 29; Magnus, Pfluger’s Arch., 102,
103, 108, 111; Baumstark and Cohnheim, Zeitschr. f. physiol. Chem., 65.
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