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 calcmel 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 (MASIUS and VANLAIR), which is identical with uro- 

 bilin (JAFFiD 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. Biologic. 35, and Poda, Micko, Prausnitz and 

 Miiller, ibid., 39. 



2 See bile-pigments, Chapter VII, and urobilin, Chapter XIV. 



