THE LIVER. 145 



animals. Human as well as ox bile has a bitter taste with a sweetish 

 after-taste. The bile of the pig and rabbit has an intense persistent 

 bitter taste. On heating bile to boiling it does not coagulate. It 

 contains (in the ox) only traces of true mucin, and its ropy proper- 

 ties depend, it seerns, chiefly on the presence of a nucleoalbumin 

 similar to mucin (PAIJKULL). The specific constituents of the bile 

 are bile-acids combined with alkalies, bile-pigments, and besides 

 small quantities of lecithin, cholesterin, soaps, neutral fats, urea,&ud. 

 mineral substances (sodium chloride, calcium and magnesium phos- 

 phate, and iron). 



Bile-salts. All bile-acids can be divided into two groups, the 

 glycocholic- and the taurocholic-acid groups. All glycocholic acids 

 contain nitrogen, but are free from sulphur and can be split with 

 the addition of water into glycocoll (amido-acetic acid) and an 

 acid free from nitrogen, cholalic acid. All taurocholic acids con- 

 tain nitrogen and sulphur and are split, with the addition of water, 

 into taurin (amido-isethionic acid) containing sulphur and cholalic 

 acid. The reason of the existence of different glycocholic and tau- 

 rocholic acids depends on the fact that there are several cholalic 

 acids. 



The different bile-acids occur in the bile as alkali salts, generally 

 in combination with sodium, but in sea-fishes as potassium salts. 

 In the bile of certain animals we find almost solely glycocholic acid, 

 in others only taurocholic acid, and in other animals a mixture of 

 both (see below). 



All alkali salts of the biliary acids are soluble in water and alco- 

 hol, but insoluble in ether. Their solution in alcohol is therefore 

 precipitated by ether, and this precipitate, with the proper care in 

 manipulation, gives, for nearly all kinds of bile thus far investigated, 

 rosettes or balls of fine needles or 4-6-sided prisms (PLATTNER'S 

 crystallized bile). Fresh human bile also crystallizes readily. The 

 bile-acids and their salts are optically active and dextro-rotary. The 

 former are dissolved by concentrated sulphuric acid at the ordi- 

 nary temperature, forming a reddish-yellow liquid which has a 

 beautiful green fluorescence. On carefully warming with concen- 

 trated sulphuric acid and a little cane-sugar, the bile-acids give a 

 beautiful cherry-red or reddish-violet liquid. PETTENKOFER'S reac- 

 tion for bile-acids is based on these facts. 



