232 PEACTICAL PHYSIOLOGY 



CHAPTER XIV. 

 THE BILE. BACTERIAL DIGESTION. 



THIS is perhaps the most puzzling secretion in the whole of physiological 

 chemistry. Its digestive action is very slight, so that it would almost 

 appear, at first sight, to be an excretion of effete products rather than a 

 useful secretion. Against such an idea, however, stands the fact that 

 it is poured into the beginning of the intestinal tract, and not into the 

 end of it, as we would expect were it an excretion. Further, many of 

 its constituents are reabsorbed into the portal blood and carried back 

 to the liver, to be re-excreted in the bile. In other words, there exists 

 a circulation of certain biliary constituents from the liver to intestine 

 by the bile, and from intestine back to liver by the portal blood. It is 

 obvious, therefore, that bile collected from a biliary fistula (produced 

 by attaching the central end of the bile duct to a wound in the 

 abdominal wall) will contain less solids than the bile obtained after 

 death from the gall bladder. 



Composition of Human Bile. In /. the bile was obtained from the 

 gall bladder of persons who had been accidentally killed, but were 

 otherwise healthy ; in //. the bile was obtained from a fistula. 



i. ii. 

 100 parts contain 



Water, 86 97 



Solids, 1.4 3 



Viz. organic salts, 9 O'9-l '8 



Mucin and bile pigment, .... 3 0'5 



Cholesterin, ...... 0'2 0'06-0'16 



Lecithin and fat, ..... O'5-l'O 0'02-0'09 



Inorganic salts, 0'8 07-0 '8 



The daily secretion amounts to about 750 c.c. To study the chemistry 

 of bile we employ that of the ox since this is easily procurable. 



EXPERIMENT I. Examine some ox bile. Note that it has a 

 green colour, a peculiar musk-like odour, a bitter-sweet taste, a faint 

 alkaline reaction to litmus paper, and that it is of a slimy con- 

 sistence. 



EXPERIMENT II. If a few drops of a weak acetic acid be added to a 

 few cubic centimetres of bile, a stringy precipitate is produced. This 

 consists in some animals (ox) of nucleo-proteid, in others (man) of 

 mucin. Filter off this precipitate, and note that the filtrate has lost its 

 slimy character. Boil the filtrate : no coagulum is produced, therefore 

 bile contains no native proteid. 



