CHEMICAL BASIS OF THE ANIMAL BODY. 173 



of the calf, as also in foetal urine and amniotic fluid ; it occurs also 

 in the urine of many animals for a short period after their birth. 

 Traces of it are sometimes detected in this excretion at a later date. 

 It is obtained in urine after the internal administration of uric acid 1 . It 

 has also been found in vegetable tissues 2 . It crystallises in small, shining, 

 colourless, hexagonal prisms. They are soluble in 160 parts of cold 

 water, more soluble in hot, insoluble in cold alcohol and ether, soluble 

 in hot alcohol. Carbonates of the alkalis dissolve them, and compounds 

 may be formed of allantoin with metals but not with acids. The salts 

 with silver and mercury are important as providing a means of 

 separating allantoin from its solutions. 



Allantoin gives no reactions which are sufficiently striking to admit 

 of its detection in urine or other fluids : it must therefore in all cases 

 first be separated out and then examined. The separation may be 

 effected in several ways, of which those more usually employed consist 

 in its precipitation with nitrate of mercury or silver 3 . From the urine 

 of calves or from their allantoic fluid, allantoin may usually be obtained 

 in crystals by mere concentration and subsequent standing till crystal- 

 lisation occurs. 



FIG. 21. CRYSTALS FROM CONCENTRATED URINE OF CALF. (After Kiihne.) 



The large central crystal composed of an aggregation of small prisms 

 is allantoin : those below it are crystals of kreatin, kreatinin and oxalate of 

 lime. The large prisms in the upper part of the figure consist of magnesium 

 phosphate. 



Preparation. Allantoin may be easily obtained by the careful 

 oxidation of uric acid with potassium permanganate 4 . It may also be 



1 Salkowski, loc. cit. 



2 Schulze u. Barbieri, Jn. f. pr. Chem. Bd. xxv. (1882), S. 145. Schulze u. 

 Bosshard, Zt. f. physiol. Chem. Bd. ix. (1885), S. 420. 



3 For details see Hoppe-Seyler, loc. cit. S. 162. Neubauer u. Vogel, loc. cit. 

 S. 222. 



4 Claus, Ber. d. d. chem. Gesell Bd. vn. 1874, S. 227. 



