32 LECTURE II. 



Glucuronic acid itself is not crystalline, but on boiling its solution, 

 glucurone lactone, C 6 H 8 O 6 , crystallizes out: 



CHO . CHOH . CH . CHOH . CHOH . CO. 

 I O 



Glucuronic acid does not occur free in the animal organism, and the 

 uncombined acid has not yet been positively identified in the vegetable 

 kingdom. Its derivatives are always present to a slight extent in urine, 

 in the blood, and in the liver. 1 It has always been found present in ester- 

 like coupling with various compounds from which the glucuronic acid may 

 be prepared by saponifying reagents. In normal urine we find phenol-, 

 indoxyl-, and skatoxyl-glucuronic acids. These compounds are of much 

 less importance than those well-known compounds of glucuronic acid with 

 different substances introduced into the body. Glucuronic acid pairs with 

 members of the aliphatic series (alcohols, aldehydes, ketones, etc.) and also 

 of the aromatic series. The best known of these compounds are those with 

 camphor and chloral, although the number of conjugated d-glucuronic 

 acids that have been studied is very large. 2 According to their entire 

 behavior they may be regarded as glucosides. 



Up to the present time, the way in which glucuronic acid is formed has 

 not been clearly decided. Again, we know nothing regarding the amount 

 formed under normal conditions, for it is highly probable that the acid is 

 oxidized further in the organism when no compound capable of combining 

 with it is present. It would seem most probable that it is formed from 

 glucose, but, as Emil Fischer 3 has stated, it is difficult to understand a 

 direct transformation here. It is hard to see why in such a case the 

 oxidation should take place at the primary alcohol group rather than at 

 the readily-oxidizable aldehyde group. Emil Fischer assumes, therefore, 

 that by the introduction of substances such as camphor, there is an inter- 

 mediate combination with the glucose so that the aldehyde group is thus 

 protected from oxidation. Then by oxidation of the free primary alcohol 

 group, the glucuronic acid compound is. formed. 



Thierf elder 4 called attention to another source of glucuronic acid by 

 showing that when camphor and chloral hydrate are fed to hungry dogs 

 the corresponding conjugated acid is eliminated in the urine. It, therefore, 



1 Paul Mayer and Carl Neuberg: Z. physiol. Chem. 29, 256 (1900). Paul Mayer: ibid. 

 32, 518 (1901). Lepine and Boulud: Compt. rend. 133, 138 (1901); 134, 398 (1902); 

 141, 453 (1905). 



" Hildebrandt has recently studied a large number of these compounds. See sum- 

 mary in article by Neuberg on Pentoses and Glucuronic Acid, Ergeb. Physiol. (Asher 

 and Spiro), 3 Abt I, p. 373. 



8 E. Fischer and O. Piloty: Ber. 24, 521 (1891). 



4 Z. physiol. Chem. 10, 163 (1886). 



