UREA. 49 



is at once sharp and sweet. It is sliglitl}^ soluble in cold, 

 but more so in hot water ; it dissolves readily in alcohol : its 

 solution reddens litmus. Most of the cholates are soluble, and 

 possess a sweetish taste. Dumas assigns to this acid the 

 formulai C^„ H^, O,,. 



There is no subject in the whole domain of animal chemistiy 

 that is more perplexing and intricate than the bile and its 

 constituents. In the preceding pages we have adopted the 

 views of Berzelius, but upon this point (cholic acid) he is very- 

 undecided. In the edition of his ^ Animal Chemistry/ pub- 

 lished in 1840, he states that he conceives it probable that 

 cholic acid is produced by bilin alone, and that any fellinic or 

 cholinic acids that may be simultaneously present take no part 

 in the metamorphosis. In his article ' Bile, ' in Wagner^s 

 ' Handworterbuch,^ published two years later, he states that 

 bilin in a state of purity undergoes only a very slight change 

 by boiling with hydrated potash, and that he could not convert 

 it into cholic acid in that manner. Cholic acid certainly does 

 not pre-exist in the bile. 



Diagnosis of hilin. Bilin may be detected by its peculiar 

 taste. It is distinguished from the previous substances by its 

 solubility in water and absolute alcohol, and by its insolubility 

 in ether. Although absolutely pure bilin is said by Berzelius to 

 be unaffected by metallic salts, basic acetate of lead and per- 

 chloride of iron throw down white precipitates from an 

 aqueous solution; the latter, on the application of warmth, 

 assumes a cinnamon tint : these reactions are probably owing 

 to the presence of bilifellinic acid. 



12. Urea. 



Urea forms the principal constituent of the solid residue 

 of normal human urine. It is found in considerable quantity 

 in the blood after extirpation of the kidneys, also in certain 

 pathological conditions in which the renal functions are not 

 properly discharged, as in diabetes, cholera, ischuria, and 

 Bright's disease. That it does exist in healthy blood as a 

 constant, although very minute constituent, has also been 

 recently proved by Marchand and Simon. Rees has detected 



' See Appendix 1, Note 17. 



4 



