268 THE BILE-ACIDS. 



When cholalic acid is boiled with concentrated HC1, or heated dry at 200 C, it 

 becomes an anhydride, thus : 



Cholalic acid . = C24H 40 O 6 , produces 

 Choloidinic acid . = C 24 Hg30 4 + H 2 0, and this again yields 

 Dyslysin . . =C 24 H 36 3 =H 2 0. 

 Choloidinic acid is, however, not improbably a mixture of cholalic acid and dyslysin ; dys- 

 lysin, when fused with caustic potash, is changed into cholalate of potash. By oxidation 

 cholalic acid yields a tribasic acid, as yet uninvestigated, and a fair amount of oxalic acid, but 

 no fatty acids (CUve). 



Pettenkoffer's Test. The bile-acids, cholic acid, and their anhydrides, when 

 dissolved in water, yield on the addition of concentrated sulphuric acid (added in 

 drops so as not to heat the fluid above 70 C), and several drops of a 10 per cent, 

 solution of cane-sugar, a reddish-purple transparent fluid, which shows two absorp- 

 tion-bands at E and F (Schenk). [A very good' method is to mix a few drops of 

 the cane-sugar solution with the bile, and to shake the mixture until a copious 

 froth is obtained. Pour the sulphuric acid down the side of the test-tube, and then 

 the characteristic colour is seen in the froth. Any albumin present must be re- 

 moved before applying the test.] 



According to Drechsel, it is better to add phosphoric acid, instead of sulphuric acid, until 

 the fluid is syrupy, then add the cane-sugar, and afterwards place the whole in boiling water. 

 When investigating the amount of bile-acids in a liquid, the albumin must be removed before- 

 hand, as it gives a reaction similar to the bile-acids, but in that case the red fluid has only one 

 absorption-band. If only small quantities of bile-acids are present, the fluid must in the first 

 place be concentrated by evaporation. 



[Hay's Test. The bile-acids or their soluble salts lower the surface-tension of fluids in which 

 they are dissolved. Throw a small quantity of sulphur (sublimed or precipitated) on the surface 

 of the fluid containing bile-acids, and if the bile-acids be present, the sulphur will at once begin 

 to sink, and will be wholly precipitated within a few minutes. {Privately communicated.)] 



The bile-acids are formed in the liver. After its extirpation, there is no ac- 

 cumulation of biliary matters in the blood. 



How the formation of the nitrogenous bile-acids is'effected, is quite unknown. They must 

 be obtained from the decomposition of albuminous materials, and it is important to note that 

 the amount of bile-acids is increased by albuminous food. Taurin contains part of the sulphur 

 of albumin ; bile-salts contain 4 to 4 *6 per cent. , which may perhaps be derived from dissolved 

 red blood-corpuscles. 



(3) The Bile-Pigments. The freshly secreted bile of man and many animals 

 has a yellowish-brown colour, due to the presence of bilirubin. When it remains 

 for a considerable time in the gall-bladder, or when alkaline bile is exposed to the 

 air, the bilirubin absorbs O and becomes changed into a green pigment, biliverdin. 

 This substance is present naturally, and is the chief pigment in the bile of herbivora 

 and cold-blooded animals. 



(a) Bilirubin (C 32 H 36 N 4 6 ) is perhaps united with an alkali ; it crystallises in 

 transparent fox-red clinorhombic prisms. It is insoluble in water, soluble in chloro- 

 form, by which substance it may be separated from biliverdin, which is insoluble 

 in chloroform. It unites as a monobasic acid with alkalies, and as such is soluble. 

 It is identical with Virchow's hajmatoidin ( 20). 



Preparation. It is most easily prepared from the red (bilirubin-chalk) gall-stones of man or 

 the ox. The stones are pounded, and their chalk dissolved by hydrochloric acid ; the pigment 

 is then extracted with chloroform. That bilirubin is derived from haemoglobin is very prob- 

 able, considering its identity with haematoidin. Very probably red blood-corpuscles are 

 dissolved in the liver, and their haemoglobin changed into bilirubin. 



(b) Biliverdin, C 32 H 36 N 4 8 , is an oxidised derivative of the former, from which 

 it can be obtained by various oxidation-processes. It is readily soluble in alcohol y 

 very slightly so in ether, and not at all soluble in chloroform. It occurs in the 

 placenta of the bitch. As yet it has not been retransformed by reducing agents 

 into bilirubin. 



Tests for Bile-Pigments, Bilirubin and biliverdin may occur in other fluids, 



