3 i2 A MANUAL OF PHYSIOLOGY 



cholalic acid, and a nitrogenous body, glycin in glycocholic, and 

 taurin in taurocholic acid. 



The decomposition of the bile-acids into these substances is 

 effected by boiling them with dilute acid or alkali, a molecule of 

 water being taken up ; thus 



C 26 H 43 N0 6 + H 2 = C 2 H 5 N0 2 + C 24 H 40 O 5 ; 



Glycocholic acid. Glycin. Chohc acid. 



C 26 H 45 NSp 7 + H 2 O = C 2 H 7 NS0 3 + C 24 H 40 O 5 . 



Taurocholic acid. Taurin. Cholic acid. 



Taurocholic acid is much more easily broken up than glycocholic ; 

 even boiling with water is sufficient. 



Glycin is amido-acetic acid, taurin is amido-isethionic acid, an 

 atom of the hydrogen of the acid being in each case replaced by 

 NH 9 . A notable difference between glycocholic and taurocholic 

 acid"is that the latter contains sulphur. The whole of this belongs 

 to the taurin. 



Traces of cholic acid, formed by hydrolysis from the bile-acids, 

 probably by the action of putrefactive bacteria, are found in the 

 intestines, especially in the lower portion. 



PettenkofeSs test for bile-acids (Practical Exercises, p. 381), acci- 

 dentally discovered in examining the action of bile upon sugar, 

 depends upon three facts: (i) That cholic acid and furfurol give a 

 purple colour when brought together ; (2) that the bile-salts yield 

 cholic acid when acted upon by sulphuric acid ; (3) that when cane- 

 sugar is decomposed by strong sulphuric acid, furfurol is formed. 



Since a similar colour is given when the same reagents are added 

 to a solution containing albumin, it is necessary to remove this, if 

 present, from any liquid which is to be tested for bile-acids. 



Lecithin and cholesterin are by no means peculiar to bile. They 

 are found in almost all the liquids of the body, and are especially 

 important constituents of the nervous substance. The former is a 

 crystallizable fat of a peculiar nature, containing nitrogen and 

 phosphorus. It is unstable, and when heated with baryta-water it 

 yields a soap, barium stearate, which is precipitated, and two other sub- 

 stances, choline and glycero-phosphoric acid, which remain in solution. 



Cholesterin is a triatomic alcohol. It is best obtained from white 

 gallstones, of which it is the chief, and sometimes almost the sole, 

 constituent (see Practical Exercises, p. 382). 



The chief inorganic salts of bile are sodium chloride, sodium car- 

 bonate, and alkaline sodium phosphate. The phosphoric acid of the 

 ash comes partly from the phosphorus of organic compounds (lecithin 

 and bile-mucin), the sulphuric acid from the sulphur of taurocholic 

 acid, the sodium largely from the bile-salts. Iron is a notable in- 

 organic constituent of bile, although it exists only in traces, in the 

 form of phosphate of iron. Manganese is also present. 100 c.c. of 

 fresh bile yields 50 to 100 c.c. of carbon dioxide, part of which is in 

 solution and part combined with alkalies. 



