DIGESTION. 223 



habitually acid (WEGSCHEIDER). The odor is perhaps chiefly due 

 to skatol, which was first found in the excrements by BRIEGER, 

 and so named by him. Indol and other substances also take part 

 in the production of odor. The color is ordinarily lighter or 

 darker brown, and depends above all upon the nature of the food. 

 Medicinal bodies may give the faeces an abnormal color. The ex- 

 crements are colored black by iron and 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 putrefaction and the decom- 

 position of the bile-pigments, so that a part of the bile-pigments 

 pass into the faeces as biliverdin. According to LESAGE, a green 

 color of the excrements in children is caused partly by biliverdin and 

 partly by a pigment produced from a bacillus. In the yolk-yellow 

 or greenish-yellow excrements of nursing infants we can detect 

 bilirubin. Neither bilirubin nor biliverdin seems to exist in the 

 excrements of mature persons under normal conditions. On the 

 contrary, we find STERCOBILIN' (MASIUS and VANLAIR), which, ac- 

 cording to certain investigators, is identical with hydrobilirubin 

 (MALY), which is obtained from bilirubin by a reduction process, 

 and urobilin (JAFFE) a view contested by MAcMuNN. Bilirubin 

 may occur in pathological cases in the faeces of mature persons. 

 It has been observed in a crystallized state (as haematoidin) in the 

 faeces of children as well as of grown persons (UFFELMANN, v. 

 JAKSCH). 



The absence of bile (acholic faeces) causes the excrements 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-pig- 

 ments. In these cases a large quantity of crystals has been ob- 

 served (GERHARDT, v. JAKSCH) which consist chiefly of magnesia 

 soaps (OESTERLEN) or sodium soaps (STADELMANN). Hemorrhage 

 in the upper parts of the digestive tract yields, when it is not 

 very abundant, a dark-brown excrement, due to haematin. 



EXCRETIN, so named by MARCET, is a crystalline bodv occurring in 

 human excrement, but which, according to HOPPE-SEYLER, is perhaps only 

 impure cholesterin. EXCRETOLIC ACID is the name given by MARCET to a 

 body similar to oil and with an excrementiteous odor. 



In consideration of the very variable composition of excrements their 

 quantitative analyses are of little value and therefore will be omitted. 



