CH. xxxiii.] JAUNDICE. 



in the fseces ; the pigment is changed into stercobilin, a substance 

 like hydrobilirubin. Some of the stercobilin is absorbed, and 

 leaves the body as the urinary pigment, urobilin (see p. 504). 



The bile-expelling mechanism must be carefully distin- 

 guished from the bile-secreting action of the liver-cells. The bile 

 is forced into the ducts, and ultimately into the duodenum, by 

 the pressure of newly-formed bile pressing on that previously in 

 the ducts, and this is assisted by the contraction of the plain 

 muscular fibres of the larger ducts and gall-bladder, which occurs 

 reflexly when the food enters the duodenum. In cases of obstruc- 

 tion, as by a gall-stone, in the ducts, this action becomes excessive, 

 and gives rise to the intense pain known as hepatic colic. 



Many so-called cholagogues (bile-drivers), like calomel, act on the 

 bile- expelling mechanism and increase the peristalsis of the mus- 

 cular tissue ; they do not really cause an increased formation of bile. 



Jaundice. The commonest form of jaundice is produced by 

 obstruction in the bile ducts preventing the bile entering the 

 intestine. A very small amount of obstruction, for instance, a 

 plug of mucus produced in excess owing to inflammatory processes, 

 will often be sufficient, as the bile is secreted at such low pressure. 

 Under these circumstances, the fseces are whitish or clay coloured, 

 and the bile passing backwards into the lymph,* enters the blood 

 and is thus distributed over the body, causing a yellow tint in the 

 skin and mucous membranes, and colouring the urine deeply. 



In some cases of jaundice, however (e.g. produced by various 

 poisons), there is no obvious obstruction ; the causes of non- 

 obstructive, or blood-jaundice, form a pathological problem of 

 some interest. A few years ago it was believed that the bile 

 pigment was actually produced in the blood. But all recent work 

 shows that the liver is the only place where production of bile 

 occurs, and that in all cases of so-called non-obstructive jaundice, 

 the bile is absorbed from the liver. There may be obstruction 

 present in the smaller ducts, or the functions of the liver may be 

 so upset that the bile passes into the lymph even when there is 

 no obstruction. 



The Glycogenic Function of the Liver. 



The important fact that the liver normally forms sugar, or a 

 substance readily convertible into it, was discovered by Claude 

 Bernard in the following way : he fed a dog for seven days with 



* The absorption is by the lymph, because if jaundice is produced in 

 nn animal l.y ligature of the bile duct, it will cease when the thoracic 

 duct is tied. 



