248 THE LIVER. 



.C 26 H 43 N0 6 + H 2 6 = C^H^O, + C 2 H 5 M) 2 . 



Glycocholic acid. Water. Cholic acid. Glycocoll. 



C^NSO, + H 2 = C 24 H 40 5 4- C 2 H 7 NSO 3 . 



Taurocholic acid. Water. Cholic acid. Taurin. 



A similar decomposition of the bile-acids is believed to take 

 place in the intestine, with the production of cholic acid. 



Pettenkofer's Test. When cane-sugar and strong sulphuric acid 

 are added to bile or a solution of bile-salts a purplish or red- 

 . dish-violet color is produced. This is due to the action of the 

 sulphuric acid on the cane-sugar, producing furfural or furfur- 

 aldehyd, and this acting upon the cholic acid gives the characteris- 

 tic color. In applying this test the temperature should be kept 

 below 70 C., and not too much cane-sugar added, otherwise it 

 will undergo carbonization. The usual way of performing this 

 test is to add to a few drops of the fluid in a porcelain capsule a 

 drop of strong sulphuric acid, and spread out the mixture ; then 

 add to this a drop of a 10 per cent, solution of cane-sugar. If 

 the color does not appear, the capsule should be warmed. Inas- 

 much as the test depends upon the reaction between furfural and 

 cholic acid, instead of using cane-sugar, a drop of a 1 : 1000 solu- 

 tion of furfural may be added to 1 c.c. of an alcoholic solution of 

 bile-salts, and to this 1 c.c. of concentrated sulphuric acid, care 

 being taken as before to keep down the temperature. It is said 

 that the presence of -^V ^ "sV ^ a milligram of cholic acid may 

 be recognized by the furfural test. 



Unfortunately, Pettenkofer's reaction alone cannot be relied 

 upon as a test for the bile-salts, inasmuch as proteids and other 

 substances to the number of forty will give the same color. The 

 color produced by cholic acid may, however, be distinguished 

 from that produced by all other substances by its spectrum ; two 

 bands, one between the solar lines D and E near to E, and the 

 other at F. The bile-acids are formed by the cells of the liver ; 

 probably from some albuminoid or proteid constituent. They are 

 absorbed by the intestine and are not excretory products, but have 

 various offices to perform and for which they are produced; just 

 what these are has not been definitely determined, but it is 

 regarded as probable that among other offices is that of dissolv- 

 ing the cholesterin, which would otherwise be insoluble. Other 

 offices will be referred to in connection with the discussion of the 

 offices of the bile as a whole. 



Cholesterin. The formula for this substance is C^H^O. It is 

 found not only in bile, but also in nervous tissue and in the cells 

 of plants and animals (p. 101), where it results from the kata- 

 bolic processes taking place in them. It is brought to the liver 

 by the blood, and is not formed in that organ. It is an excretory 



