COMPOSITION OFFICES. 473 



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 biliverdin, 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. 



Reaction. 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. 

 Gamgee 3 states that the faeces in man are normally alkaline, and very 

 exceptionally present an acid reaction. Wegscheider 4 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 they 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 iiucleins from nucleo-proteids, keratin from epidermal struc- 

 tures, and haematin from haemoglobin. 



The mineral salts present vary with the food, 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 faeces is due to 

 hydrobilirubin ; Hammarsten ("Lehrbnch der physiol. Chemie," Ann. 3, S. 283), that the 

 decomposition products of the bile pigments have little influence on the normal colour of 

 the faeces. 



" Lehrbuch der physiol. Chemie," Aufl. 3, S. 284. 



3 "Physiological Chemistry of the Animal Body," vol. ii. p. 457. 



4 Jahresb. u. 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 faeces ; this is shown by an experiment due to Hermann (Arch. f. d. ges. 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 faeces in appearance. 



