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516 DIGESTION.
originates partly from the contents of the stomach, partly from the
putrefaction of the proteins, partly from the lactic-acid and butyric-
acid fermentation of carbohydrates, and partly from the setting free of
carbon dioxide from the alkali carbonates of the pancreatic and intes-
tinal juices by their neutralization through the hydrochloric acid of
the gastric juice and by organic acids formed in the fermentation.
Hydrogen occurs in largest quantities after a milk diet, and in smallest
quantities after a purely meat diet. This gas seems to be formed
chiefly in the butyric-acid fermentation of carbohydrates, although it
may occur in large quantities in the putrefaction of proteins under certain
circumstances. There is no doubt that the methylmercaptan and sul-
phureted hydrogen which occur normally in the intestine originate from
the proteins. The marsh-gas undoubtedly originates in the putrefac-
tion of proteins. As proof of this Ruge * found 26.45 per cent marsh-
gas in the human intestine after a meat diet. He found a still greater
quantity of this gas after a vegetable (leguminous) diet; this coincides
with the observation that marsh-gas may be produced by a fermentation
of carbohydrates, but especially of cellulose (Tappeiner 2
) . Such an
origin of marsh-gas, especially in herbivora, is to be expected. A small
part of the marsh-gas and carbon dioxide may also arise from the decom-
position of lecithin (Hasebroek 3
).
Putrefaction in the intestine not only depends upon the composi-
tion of the food, but also upon the albuminous secretions and the bile.
Among the constituents of bile which are changed or decomposed, , there
are not only the pigments—the bilirubin yields urobilin and a brown
pigment—but also the bile-acids, especially taurocholic acid. Glyco-
cholic acid is more stable, and a part is found unchanged in the excre-
ment of certain animals, while taurocholic acid is so completely decom-
posed that it is entirely absent in the feces. In the fetus, on the con-
trary, in whose intestinal tract no putrefaction processes occur, undecom-
posed bile-acids and bile-pigments are found in the contents of the
intestine. The transformation of bilirubin into urobilin does not occur,
as previously stated, in the small, but in the large intestine in man.
As under normal conditions no putrefaction, or a,t least none worth
mentioning, occurs in the small intestine, and as often nearly all the pro-
tein of the food is absorbed, it follows that ordinarily it is the secretions
and cells rich in proteins which undergo putrefaction. That the secre-
tions rich in proteins are destroyed in putrefaction in the intestine
1
Wien. Sitzungsber., 44.
2
Zeitschr. f. Biologie., 20 and 24.
3
Zeitschr. f. phyaiol. Chem., 12.
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