510 THE LIVER [OIL XXXIII. 



Bile Mucin. -There has baen considerable diversity of opinion 

 as to whether bile mucin is really mucin. The most recent work in 

 Hammarsten's laboratory shows that differences occur in different 

 animals. Thus in the ox there is very little true mucin, but a great 

 amount of nucleo-proteid ; in human bile, on the other hand, there 

 is very little if any nucleo-proteid ; the mucinoid material present 

 there is really mucin. 



The Bile Salts. The bile contains the sodium salts of complex 

 amino-acids called the bile acids. The two acids most frequently 

 found are glycocholic and taurocholic acids. The former is the more 

 abundant in the bile of man and herbivora ; the latter in carnivorous 

 animals, like the dog. The most important difference between the 

 two acids is that taurocholic acid contains sulphur, and glycocholic 

 acid does not. 



Glycocholic acid (C 26 H 43 N0 6 ) is by the action of dilute acids and 

 alkalis, and also in the intestine, hydrolysed and split into glycine or 

 amino-acetic acid and cholalic acid. 



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



[Glycocholic acid.] [Glycine.] [Cholalic acid.J 



The glycocholate of soda has the formula C 26 H 4;2 NaN0 6 . 

 Taurocholic acid (C 26 H 45 N0 7 S) similarly splits into taurine or 

 amino-isethionic acid and cholalic acid. 



C 26 H 45 N0 7 S + H 2 = C 2 H 7 N0 3 S + C 24 H 40 O 5 



[Taurocholic acid.] [Tauriue.] [Cholalic acid.] 



The taurocholate of soda has the formula C 96 H 44 NaN0 7 S. 



The colour reaction called Pettenkofer's reaction, is due to the 

 presence of cholalic acid. Small quantities of cane sugar and strong 

 sulphuric acid are added to the bile. The sulphuric acid acting on 

 sugar forms a small quantity of a substance called furfuraldehyde, in 

 addition to other products. The furfuraldehyde gives a brilliant 

 purple colour with cholalic acid. 



The Bile Pigments. The two chief bile pigments are bilirubin 

 and biliverdin. Bile which contains chiefly the former (such as dog's 

 bile) is of a golden or orange-yellow colour, while the bile of many 

 herbivora, which contains chiefly biliverdin, is either green or bluish- 

 green. Human bile is generally described as containing chiefly 

 bilirubin, but there have been some cases described in which biliverdin 

 was in excess. The bile pigments show no absorption bands with 

 the spectroscope; their origin from the blood pigment has already 

 been stated. 



Bilirubin has the formula C 16 H 18 N" 2 3 : it is thus an iron-free 

 derivative of haemoglobin. The iron is apparently stored up in the 

 liver cells, perhaps for future use in the manufacture of new haemo- 

 globin. The bile contains only a trace of iron. 



