746 UREA AND ITS ALLIES. [App. 



its purity, by the researches of later observers. According to Liebreich 1 

 and Diakonow 2 , it is a glucoside 3 . 



Cerebrin is a light, colourless, exceedingly hygroscopic powder, which 

 swells up strongly in water, slowly in the cold, rapidly on heating. 

 When heated to 80 C. it turns brown, and at a somewhat higher tempe- 

 rature melts, bubbles up and finally burns away. It is insoluble in cold 

 alcohol, or aether; warm alcohol dissolves it easily. Heated with 

 dilute mineral acids, cerebrin yields a sugar-like body, possessing left- 

 handed rotation, but incapable of fermentation. 



Preparation. Eor this see W. Miiller*. 



NITROGENOUS METABOLITES. 

 THE UREA GROUP, AMIDES, AND SIMILAR BODIES. 



Urea. (NH 2 ) 2 CO. 



The chief constituent of normal urine in mammalia, and some other 

 animals; the urine of birds also contains a small amount. Normal 

 blood, serous fluids, lymph and the liver, all contain the same body in 

 traces. It is not found in the muscles, as a normal constituent, but 

 may make its appearance there under certain pathological conditions. 



When pure it crystallises from a concentrated solution in the form 

 of long, thin glittering needles. If deposited slowly from dilute 

 solutions, the form is that of four-sided prisms with pyramidal ends; 

 these are always anhydrous. It possesses a somewhat bitter cooling 

 taste, like saltpetre. It is readily soluble in water and alcohol, the 

 solutions being neutral. In anhydrous aether it is insoluble. The 

 crystals may be heated to 120C. without being decomposed; at a 

 higher temperature they are first liquefied and then decompose, leaving 

 no residue. Heated with strong acids or alkalis, decomposition ensues, 

 the final products being carbonic anhydride and ammonia. The same 

 decomposition may also occur as the result of the action of a specific 

 ferment on urea in an aqueous solution 5 . Nitrous acid at once decom- 

 poses it into carbonic anhydride and free nitrogen. It readily forms 

 compounds with acids and bases; of these the following are of im- 

 portance. 



Nitrate of urea. (NH 2 ) 2 CO. HNO 3 . 



Crystallises in six-sided or rhombic tables. Insoluble in aether and 

 nitric acid, soluble in water, slightly soluble in alcohol. 



1 Arcli. f. patkol. Anat. Bd. 39 (1867). 



2 Centralb. f. d. med. Wiss. 1868, Nr. 7. 



3 See also, Geogheghan, Zeitsch.f. physiol. Chem. Bd. in. (1879) S. 332. 



4 Op. cit. 



6 Musculus, Pfliiger's Archiv, Bd. xu. (1876) S. 214. Jaksch. Zeitsch.f. physiol. 

 Chem. Bd. v. (1881) S. 395. 



