124 BIOLOGICAL CHEMISTRY 



contents is a ring of muscle round the pyloric end of the 

 stomach. Increase of acid in the stomach tends to cause this 

 ring to relax, whilst acid in the duodenum and solid particles in 

 the stomach tend to cause it to contract. During digestion 

 the solid particles diminish and the acid increases, hence we 

 have an increasing tendency for the pylorus to relax. As 

 soon as any of the contents of the stomach escape into the 

 duodenum, the acid in the duodenum causes the pylorus to 

 close and remain closed until the acid is neutralised. Boldyreff 

 says that excess of acid will cause such a violent contraction of 

 the duodenum that the alkaline duodenal contents will be 

 forced into the stomach and thus prevent too great an acidity 

 in the stomach.* (See p. 120.) 



Digestion in the Duodenum 



Two secretions are mixed with the food in the duodenum, 

 the bile from the liver and the pancreatic juice from the 

 pancreas. Both these are alkaline and are useful in neutralis- 

 ing the acid of the gastric contents. The bile contains no 

 enzymes but it aids the action of the enzymes that are found 

 in the pancreatic juice. 



Bile. The analysis of bile shows marked differences in 

 composition. If a fistula is made so that the bile drains away 

 and is lost the bile becomes very dilute, hence we find that 

 fistula bile is more dilute than bile obtained from the gall- 

 bladder by operation. 



TABLE XXV 



Composition of Human Bile f in parts per 1,000 by weight. 



Bladder bile. Fistula bile. 



Bile salts 97-0 10-1 



Mucin and pigments ... 41-9 



Cholesterol 9-86 



Fat 1-9 



Soaps 1 1 -2 



Lecithin 2-23 



Total solids 170*3 



Inorganic 



Water 829-7 



Fatty acids 



4-86 

 2-61 

 6-85 

 2-6 

 6-42 

 29-8 

 9-2 



970-2 



I '2 



The bile pigments are waste products from the decomposi- 

 tion of haemoglobin. They give coloured reactions, due to oxi- 

 dation, with nitric acid,| iodine, etc. Thus if some bile is 



* W. Boldyreff, Evgeb. d. PhysioL, 1911, vol. n, p. 156. 

 t J. Rosenbloom, Journ. of BioL Chem., 1913, vol. 14, p. 241. 

 J T. Tiedemann and L. Gmelin, Die Verdauung nach Versuchen, 

 1826, vol. i, p. 80. 



