CH. XXXIII.] THE BILE 513 



what it does not receive back from the intestine. Schiff was the first 

 to show that if the bile is led back into the duodenum, or even if the 

 animal is fed on bile, the percentage of solids in the bile excreted is 

 at once raised. It is on these experiments that the theory of a bile 

 circulation is mainly founded. The bile circulation relates, however, 

 chiefly, if not entirely, to the bile salts : they are found but sparingly 

 in the faeces ; they are only represented to a slight extent in the urine : 

 hence it is calculated that seven-eighths of them are re-absorbed from 

 the intestine. Small quantities of cholalic acid, taurine, and glycine 

 are found in the fasces ; the greater part of these products of the decom- 

 position of the bile salts is taken by the portal vein to the liver, where 

 they are once more synthesised into the bile salts. Some of the taurine 

 is absorbed and excreted as tauro-carbamic acid in the urine. Some of 

 the absorbed glycine may be excreted as urea or uric acid. The 

 cholesterin and mucus are found in the faeces ; the pigment is changed 

 into stercobilin (see p. 511). 



The bile-expelling mechanism must be carefully distinguished 

 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 obstruction, 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 

 muscular 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 pro- 

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

 pressure. Under these circumstances, the faeces 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 somo 

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



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

 animal by ligature of the bile duct, it will cease when the thoracic duct is tied. 



2 K 



