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522 DIGESTION.
of intestine collects material similar to feces. These masses are rich
in mineral substances and especially rich in bodies soluble in alcohol-
ether, among which cholesterin occurs, as previously mentioned (Chap-
ter VII). With a mixed diet with an excess of meat, the human feces
consist only in small part of food residues and consist in great part,
or after meat or milk diet, almost entirely, of intestinal secretions. Many
foods, therefore, produce a large quantity of feces chiefly by causing an
abundant secretion. 1
The reaction of the feces is very variable, but in man with a mixed
diet it is neutral or faintly alkaline. It is often acid in the inner part,
while the outer layers in contact with the mucous coat have an alka-
line reaction. In nursing infants it is habitually acid. The odor is
perhaps chiefly due to skatol, which was first found in the feces by
Brieger, and so named by him. Indol and other substances also take
part in the production of odor. The color is ordinarily light or dark
brown, and depends above all upon the nature of the food. Medicinal
bodies may give the feces an abnormal color. The excrement is col-
ored black by bismuth, yellow by rhubarb, and green by calomel. This
last-mentioned color was formerly accounted for by the formation of a
little mercury sulphide, but now it is said that calomel checks the putre-
faction and the decomposition of the bile-pigments, so that a part of the
bile-pigments passes into the feces as biliverdin. In the yolk-yellow or
greenish-yellow excrement of nursing infants one can detect bilirubin.
Neither bilirubin nor biliverdin seems to exist in the excrement of mature
persons under normal conditions. In adults under normal conditions
the feces contain neither bilirubin nor biliverdin. On the contrary, there
is found stercobilin (Masitjs and Vanlair), which is identical with uro-
bilin (Jaff£ 2
). Bilirubin may occur in pathological cases in the feces
of mature persons. It has been observed in a crystallized state (as
hsematoidin) in the feces of children as well as of grown persons.
The absence of bile (acholic feces) causes the feces to have, as above
stated, a gray color, due to large quantities of fat; this may, however,
be partly attributed to the absence of bile-pigments. In these cases
a large quantity of crystals has been observed which consist principally
of magnesium soaps or sodium soaps. Hemorrhage in the upper parts
of the digestive tract yields, when it is not very abundant, a dark-brown
excrement, due to haematin.
1
In regard to the constitution of feces with various foods, see Hammerl, Kermauner,
Moeller, and Prausnitz, Zeitschr. f. Biologie. 35, and Poda, Micko, Prausnitz and
Mtiller, ibid., 39.
2
See bile-pigments, Chapter VII, and urobilin, Chapter XIV.
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