396 THE LIVER. 



substance, scymnol (C 27 H 48 5 ), which gives the characteristic color reactions of 

 cholic acid. 



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

 the sodium compounds, even in sea-fishes, although this is contrary to 

 the earlier observations (ZANETTi 1 ). 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 alcohol, 

 but insoluble in ether. Their solution in alcohol is therefore precipitated 

 by ether, and this precipitate, with proper care in manipulation, gives, 

 for nearly all kinds of bile thus far investigated, rosettes or balls of fine 

 needles or four- to six-sided prisms (PLATTNER'S crystallized bile). Fresh 

 human bile also crystallizes readily. The bile-acids and their salts 

 are optically active and dextrorotatory. The salts of the different bile- 

 acids act somewhat differently toward neutral salts. The alkali salts 

 x)f the ordinary and best-studied bile-acids from man, ox, and dog are, 

 according to TENGSTROM, 2 precipitated by ammonium and magnesium 

 sulphates, and also, in pure form, by sodium nitrate and sodium chloride 

 (added to saturation). Potassium and sodium sulphates do not precip- 

 itate them. The alkali salts cannot be directly precipitated from the 

 bile by NaCl, on account of the presence of bodies retarding precipita- 

 tion, among which we find oil-soaps. 



The bile-acids are dissolved by concentrated sulphuric acid at the 

 ordinary temperature, forming a reddish-yellow liquid which has a beautiful 

 green fluorescence. According to PREGL an oxidation with a reduction 

 of the sulphuric acid into sulphur dioxide takes place. The fluorescent 

 substance has been called dehydrocholan (see below) by PREGL. 3 On 

 carefully warming with concentrated sulphuric acid and a little cane- 

 sugar, the bile-acids give a beautiful cherry-red or reddish-violet liquid. 

 PETTENKOFER'S reaction for bile-acids is based on this behavior. 



PETTENKOFER'S test for bile-acids is performed as follows: A small 

 quantity of bile in substance is dissolved in a small porcelain dish in con- 

 centrated sulphuric acid and warmed, or some of the liquid containing 

 the bile-acids is mixed with concentrated sulphuric acid, taking special 

 care in both cases that the temperature does not rise higher than 60-70 

 C. Then a 10 per cent solution of cane-sugar is added, drop by drop, 

 continually stirring with a glass rod. The presence of bile is indicated 

 by the production of a beautiful red liquid, whose color does not disap- 

 pear at the ordinary temperature, but becomes more bluish violet in 



1 See Chem. Centralbl., 1903, 1, 180. 



2 Zeitschr. f. physiol. Chem., 41. 

 3 Zeitschr. f. physiol. Chem., 45. 



