214 BILE ACIDS. 



proteids are precipitated and thus further exposed to the action of the 

 digestive enzymes 1 . It is also possessed of powerful antiseptic pro- 

 perties 2 . 



The acids obtained from the bile of different animals differ slightly in properties 

 and composition, dependently, as already stated, upon the differences between the 

 several forms of cholalic acid with which either the glycin or taurin is respectively 

 united. 



Pettenkofer's reaction for bile acids 3 . 



The following is the more usual method of obtaining the reaction. 

 Bile, which may be very considerably diluted, or a dilute solution of 

 bile-salts or acids is mixed in a porcelain dish with a few drops of a 

 10 p. c. solution of cane-sugar. Concentrated sulphuric acid is now 

 added to the mixture with constant stirring to an extent not exceeding 

 of its volume, the addition of the acid being so regulated that the 

 temperature of the mixture is not allowed to rise above 70 C. Here- 

 upon a brilliant cherry-red colour makes its appearance and rapidly 

 assumes a magnificent purple tint. On standing for some time the 

 colour becomes darker and of a more distinctly blue tint. The reaction 

 may also be obtained by the addition of first the acid and then the 

 sugar solution. The success of the test depends on the careful 

 avoidance of any excessive rise of temperature during the addition of 

 the sulphuric acid and more especially of any excess of sugar which by 

 being charred by the acid gives a brown colouration and masks the 

 typical purple 4 . The purple solution if diluted with alcohol (not with 

 water which destroys the colour) shows with a spectroscope a charac- 

 teristic absorption spectrum consisting of two absorption bands, one 

 between D and E abutting on E and a second adjoining the F line. 

 In the earlier stages of the reaction a third narrow band near D makes 

 its appearance but disappears later on 5 . 



Pettenkofer's reaction depends upon the presence in all bile-acids of 

 their cholalic acid constituent. On the first addition of sulphuric acid, 

 if the solution be at all concentrated, a white precipitate may often be 

 observed consisting of cholalic acid ; this is dissolved on the further 



1 Maly u. Emich, Monatshefte f. Chem. Bd. iv. (1883), S. 89. See also 

 Hammarsten, Pfliiger's Arch. Bd. in. (1870), S. 53. On the similar behaviour of 

 taurocholic acid to gelatin and its peptones see Emich, Monatshefte f. Chem. 

 Bd. vi. (1885), S. 95. 



2 Maly u. Emich, loc. cit. See also Lindberger, (Swedish). See Abstr. in 

 Maly's Jahresb. 1884, S. 334. 



3 Pettenkofer, Annal. d. Chem. u. Pharm. Bd. LII. (1844), S. 90. 



4 To avoid this Drechsel recommends the employment of phosphoric acid (5 of 

 glacial acid to 1 of water) instead of sulphuric acid, Jn. f. prakt. Chem. Bd. xxiv. 

 (1881), S. 44 ; xxvu. (1883), S. 424. In this case the solution must be heated by 

 immersion in boiling water. 



5 Schenk. See ref. in Maly's Jahresb. 1872, S. 232. Udranszky, Zt. f. physiol. 

 Chem. Bd. xn. (1888), S. 372. Mac Munn, Clin. chem. of urine, 1889, p. 174. 



