172 



ALLANTOIN. 



4. Allantoin. C 4 H 6 N 4 8 . (Diureide of glyoxylic acid.) 



The characteristic constituent of the allantoic fluid, more espe- 

 cially 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 administra- 

 tion 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. Car- 

 bonates 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. 



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 kreatiri, kreatinin and oxa- 

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

 of magnesium phosphate. 



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 separa- 

 tion 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 concentra- 

 tion and subsequent standing till crystallisation occurs. 



1 Salkowski, loc. cit. 



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

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



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

 S. 222. 



