THE FOOD AND DIGESTION 345 



be greater than when the diet is low. In fever there is a very 

 marked fall in the secretion, the fluid flowing from a fistula 

 becoming colourless and almost devoid of bile salts and pig- 

 ments. Certain drugs markedly modify the formation of 

 bile the salts of the bile acids stimulating the liver to form 

 more solids and to secrete more water, the salicylates acting 

 in much the same way, and all drugs which cause haemolysis 

 i.e. the solution of the pigment of the erythrocytes pro- 

 ducing an increased formation of bile pigments. 



Influence of Nerves upon the Flow of Bile (a) Expulsion 

 of Bile. There is good evidence that fibres pass to the muscles 

 of the bile passages and may cause an expulsion of bile by 

 stimulating them to contract. 



(b) Secretion of Bile. There is no evidence that nerve 

 fibres act directly upon the secretion of bile. This 

 appears to be governed by the nature of the material 

 brought to the liver by the blood and by the activity of 

 the liver cells. 



3. Mode of Formation of Bile. It has been seen that the 

 bile salts and pigments are actually formed in the liver cells, 

 and there is good evidence that the water of the bile is not 

 a mere transudation but is the product of the living activity 

 of these cells. The pressure under which bile is secreted 

 may be determined by fixing a canula in the bile duct or in 

 a biliary fistula. In man the pressure is as much as 20 to 

 30 mm. Hg, while the pressure in the portal vein of the dog 

 is only 7 to 16 mrn. Hg. 



4. Nature of Bile. Bile is not a secretion of any import- 

 ance in digestion. It has no action on proteids or carbo- 

 hydrates, and its actions on fats is merely that of a solvent. 

 Its secretion in relationship to food does not indicate that it 

 plays an active part in digestion. It is formed during intra- 

 uterine life and during fasting, and it is produced many 

 hours after food is taken, when digestive secretions are no 

 longer of use in the alimentary canal. Digestion can go on 

 quite well without the presence of bile in the intestine, 

 except that the fats are not so well absorbed. The composi- 

 tion of bile strongly suggests that it is a waste product. The 



