COMPOSITION OF KE CES. 4 7 3 
causes the faeces to have a yellowish or clay-coloured appearance. 
Such fatty stools also result when imperfect fat absorption is caused by 
stoppage of the bile duct. The derivatives of bile pigments also con- 
tribute to the colour of the faeces, 1 and part of the brown colour of 
normal faeces arises from these, although it is probably due in greater 
measure to haematin. Administration of calomel, by arresting bacterial 
decomposition, prevents the reduction of the bile pigment, which then 
appears in the faeces as biliverdiu, and produces a green colour. The 
similar colour of meconium shows that bacteria are absent in the foetal 
intestine. Green-coloured faeces are also excreted for some time after 
birth, until the normal bacteria of the intestine gradually acquire 
possession, when the biliverdin is reduced and the faeces assume a brown 
colour. 
Junction. — The reaction of the faeces is also variable. According to 
Hammarsten,' 2 they may often be alkaline on the surface, from contact 
with the intestinal mucous membrane, while acid within the mass. 
Garngee 3 states that the faeces in man are normally alkaline, and very 
exceptionally present an acid reaction. Wegscheider i found the faeces 
normally acid in infants. 
Composition. — The faeces are an exceedingly complex mixture, con- 
taining substances of various origin and constitution, soluble and 
insoluble, derived from the food, the bile, and the detritus of the in- 
testinal surface. 5 The number of these components is so large, and the 
amounts in which the}' are present so variable, that tables of quantitative 
composition possess little value. 
The undissolved substances consist of fragments of undigested food, 
such as pieces of vegetables, muscle fibres, connective tissue, elastic 
fibres, and small masses of casein and fat. The amount of these is 
largely increased when the supply of food taken in is more than 
sufficient to satisfy the demands of the body. A microscopic examina- 
tion further shows epithelial cells derived from the intestine, starch 
granules, fat globules, and occasionally crystals of magnesium and 
calcium phosphates, and of ammonia-magnesium phosphate. Besides 
these, there is present the indigestible residue of various foodstuffs, 
such as nucleins from nucleo-proteids, keratin from epidermal struc- 
tures, and haematin from haemoglobin. 
The mineral salts present vary with the fond, but consist chiefly of 
the phosphates of the alkaline earths, with small quantities of silica and 
phosphate of iron. 
The other constituents include mucin, derived from the various 
secretions, mainly from the mucous membrane of the intestine ; indol, 
skatol, volatile fatty acids, ammonia, sulphuretted hydrogen, and methane, 
1 There is some difference of opinion on this point. Gamgee (" Physiological Chemistry of 
the Animal Body," vol. ii. p. 458) states that the brown colour of normal feces is due to 
hydrobilirubin ; Hammarsten ("Lehrbuch der physiol. Chemie," Aufl. 3, S. 283), that the 
decomposition products of the bile pigments have little influence on the normal colour of 
2 "Lehrbuch der physiol. Chemie," Aufl. 3, S. 284. 
3 "Physiological Chemistry of the Animal Body," vol. ii. p. 457. 
4 Jahresb. ii. d. Fortschr. d. Thier-Chem., Wiesbaden, 1876, Bd. vi. S. 482. 
5 The mucous membrane of the intestine and its secretion furnish a considerable quota 
to the feces ; tins is shown by an experiment due to Hermann (Arch./. J. >jes. Physiol., 
Bonn, 1890, Bd. xlvi. S. 93), who separated a loop of intestine, cleared it of contents, sewed 
its two ends together so that it formed a ring, restored the continuity of the remainder of 
the intestine, and closed the wound. In a few days it was found, on killing the animal, 
that this loop was filled with a mass resembling feces in appearance. 
