APP.] CHEMICAL BASIS OF THE ANIMAL BODY. 7G3 



To avoid confusion it is now best to use the term 'cholic' as a synonym for 

 ' cholalic,' Demarcay who first (1838) described the cholalic acid as a product of the 

 decomposition of bile acids having given it the name of cholic acid. The name 

 cholalic is perhaps the best, since it indicates the method by which the bile acids are 

 split up, viz. by treatment with alkali. 



This is the principal bile-acid of ox gall; it is also present in the 

 bile of man, but has so far not been observed in that of carnivora. In 

 icterus, the urine may contain traces of this acid. 



It crystallises in fine, glistening needles. These are slightly soluble 

 in cold water, readily so in hot water and alcohol but insoluble in sether. 

 They possess a bitter and yet sweet taste, aud a strong acid reaction. 



The salts of this acid are readily soluble in water and crystallise 

 well. The salts, as well as the free acid, exert right-handed polarisation 

 amounting to + 29*0 for the acid, and + 257 for the sodium salt, both 

 measured for yellow light. 



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

 Cholalic acid. Glycin. Glycocholic acid. 



CH^O B + C. 2 NH 5 2 - H 2 = CJEJ^NO, 



Prolonged boiling with dilute mineral acids or caustic alkalis decomposes gly- 

 cocholic 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, C 26 H 41 N0 5 . 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 evaporating to a syrup, decolorising 

 with animal charcoal, extracting with strong alcohol, and precipitating 

 by a large excess of sether. Its separation from taurocholic acid depends 

 on its precipitation by normal lead acetate, taurocholic acid not being 

 precipitated by this reagent 



Taurocholic acid. C^H^NSO^ 



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

 bile and that of carnivora, notably of the dog. 



It crystallises with difficulty in very fine needles which are exceed- 

 ingly deliquescent. When dried it is an amorphous powder, with 

 pure bitter taste, easily soluble in water and alcohol, insoluble in sether. 

 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 decom- 

 posed if boiled with water. The products of decomposition are tauriu 

 and cholalic acid. 



