CHEMICAL BASIS OF THE ANIMAL BODY. 91& 



Glycocholic acid is a compound of glycin and cholalic acid ; thus : 

 Cholalic acid. Glycin. Glycocholic acid. 



C 24 H 40 5 + C 2 NH 5 - H 2 = C 26 H 43 N0 6 . 



Prolonged boiling with dilute mineral acids or caustic alkalies decomposes glycocholic acid 

 into glycin and cholalic acid ; if dissolved in concentrated sulphuric acid and then warmed, 

 glycocholic acid by the removal of one molecule of water yields cholonic acid, CsoH^NOs. The 

 barium salt of this last acid is insoluble in water, which fact is of importance, since cholonic 

 acid possesses nearly the same specific rotatory power as glycocholic acid. 



Preparation. From ox-gall by evaporation to a syrup, decolorizing with animal 

 charcoal, extracting with strong alcohol, and precipitating by a large excess of ether. 

 Its separation from taurocholic acid depends on its precipitation by normal lead 

 acetate, taurocholic acid not being precipitated by this reagent. 



Taurocholic Acid. C 26 H 45 NS0 7 . 



Occurs also in ox-gall, but is found especially plentiful in human bile and that 

 of carnivora, notably of the dog. 



It crystallizes with difficulty in very fine needles, which are exceedingly deliques- 

 cent. When dried it is an amorphous powder, with pure bitter taste, easily sol- 

 uble in water and alcohol, insoluble in ether. All its salts are soluble in water, and 

 are precipitated by basic lead acetate in the presence of free ammonia. The sodium 

 salt dissolved in alcohol has a specific rotatory power of +24.5 ; if dissolved in 

 water this rotation is less, and in this respect it resembles glycocholic acid. 



This acid is far more unstable than the preceding one, being decomposed if 

 boiled with water. The products of decomposition are taurin and cholalic acid. 



Taurocholic acid is a compound of taurin and cholalic acid ; thus : 



Cholalic acid. Taurin. Taurocholic acid. 



C 24 H 40 5 + C 2 H 7 N0 3 S -H 2 = C 26 H 45 N0 7 S. 



Preparation. From the bile of dogs by a process similar to that for glycocholic 

 acid. It is separated from traces of this latter and from cholalic acid by precipita- 

 tion with basic lead acetate and ammonia. 1 



BILE PIGMENTS. 

 Bilirubin. C 16 H 18 N 2 3 . 



It is found chiefly in the fresh bile of man and carnivora, to which it gives the 

 characteristic dark golden-red color. It frequently constitutes a considerable part 

 of some kind of gall-stones, not, however, as free bilirubin, but as a compound with 

 earthy matter, chiefly chalk ; the gall-stones of oxen and pigs often contain 40 per 

 cent, of this compound. 2 These are, therefore, the best material from which to 

 prepare bilirubin. 



Preparation. The gall-stones are treated with strong acetic or dilute hydro- 

 chloric acid, to separate the earthy matter, and the residue is thoroughly washed 

 with water and alcohol and dried. From this residue the prolonged action of hot 

 chloroform extracts the bilirubin, which may either be obtained in the amorphous 

 form by precipitation with alcohol of its solution in chloroform, or as well-defined 

 crystals by the slow evaporation of the chloroform solution. 



The most usual form of the crystals is that of rhombic prisms ; they are readily 

 soluble in chloroform and alkaline solutions only. 



By treatment with oxidizing agents, such as nitrous acid, bilirubin takes up 

 oxygen and becomes biliverdin, the color at the same time changing to green. The 

 possible oxidation does not end here, and if continued a series of products are ob- 

 tained, each with a characteristic color, as in the well-known Gmelin's test. 3 Of 

 these only the final product of the oxidation has been obtained in a state of suffi- 

 cient purity to enable any definite statements to be made of its characteristics.* 



This is the body known as Choletelin (see below). 



1 Parke, Tubing. Med.-chem. Unters., Bd. i., S. 160. 



2 Maly, Sitzber. d. Wien. Akad., Bd. Ivii. (1868), ii. Abth., Febr. Hft. 



3 Tiedmann u. Gmelin, Die Verdauung, 1826, S. 79. 



4 Heynsius u. Campbell, Pfliiger's Arch., Bd. iv. (1871), S. 497. 



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