274 THE ANIMAL. XII. 



of the carnivora, and also occurs, in combination with calcium, 

 in gall-stones. On exposure to air, alkaline solutions absorb 

 oxygen and become green (biliverdin). 



Biliverclin, C 16 H 18 N 2 4 , is an amorphous green substance, 

 insoluble in water but soluble in alcohol and in alkalies. It is 

 found in bile, in shells of birds' eggs, and sometimes in gall- 

 stones. Other colouring substances have been found in bile. 



The mineral matters include potassium, sodium, calcium, 

 magnesium, iron, and often traces of copper and zinc ; phos- 

 phates and chlorides are also present. 



Bile undoubtedly plays an important part in the digestion 

 of fats. If the bile be prevented from entering the alimentary 

 canal the faeces become light-coloured, much more putrescent, 

 and contain a large amount of fat. Bile has a slight solvent 

 power upon fats, as is evidenced by the well-known use of 

 ox-gall for removing greasy stains from textile fabrics. It also 

 possesses, in a well-marked degree, the property of aiding the 

 pancreatic juice in bringing about the emulsifi cation of fats ; 

 this is probably by virtue of its alkalinity and the power 

 possessed by bile acids and their salts of dissolving lime soap 

 and cholesterin. Bile is said to be possessed of antiseptic 

 properties and to regulate the putrefaction which occurs in the 

 intestines. It is also a laxative. 



Bile is to a large extent reabsorbed in the intestines and 

 only a portion is expelled in the faeces. 



The Faeces of an animal contain the undigested portions of its 

 food, together with the products of their decomposition under 

 the influence of the enzymes and bacteria present in the 

 alimentary canal, and some portions of the digestive fluids 

 themselves ; mucus and epithelial cells from the walls of the 

 intestines are also present. 



Small quantities of fat, cholesterin, and calcium and mag- 

 nesium salts of fatty acids also occur, while the specific odour 

 is due to the presence of skatol and indol or their derivatives, 

 though sometimes sulphuretted hydrogen, ammonia, amines, 

 and other volatile substances are present. A dark brown 

 reduction product of bilirubin known as liydro-bilirubin, 

 7 , is said to be often present. 



