256 THE URINE. 



1-2 c.c. of a 10 per cent, solution of calcium chloride and acetic 

 acid. The process is continued as described. 



With human urine larger quantities, such as 500 c.c., are em- 

 ployed, which are first concentrated to about one-third of their 

 original volume. 



A 11 an to in. 



Allantoin is a normal constituent of the urine of man, as also 

 of various animals, but is usually present only in traces in the 

 adult, while during the first weeks of life it is more abundant. 

 Larger amounts also occur during pregnancy. Aside from the 

 urine, it is found in the amniotic fluid and in the allantoic fluid of 

 cows. Like oxaluric acid, it is an oxidation-product of uric acid, 

 and Salkowski demonstrated that an increased elimination occurred 

 in dogs when uric acid was ingested. An artificial increase is 

 similarly observed in poisoning with hydrazin, and we can readily 

 understand that in consequence of the degenerative changes which 

 are thus produced in the liver the oxidation-processes are accordingly 

 diminished, and allantoin results. 



The formation of allantoin from uric acid may be represented by 

 the equation : 



/NH.CH.NH.CO.NH, 



C 5 H 4 N 4 3 + H 2 + O = CO/ 4- C0 2 



X NH.CO 



Uric acid. Allantoin. 



It is a glyoxyl-diureid, and may be produced artificially by 

 heating glyoxylic acid and urea together at a temperature of 100 C. 

 The reaction then takes place according to the equation : 



/NH 2 COH /NH 2 /NH.CH.NH.CO.NH,, 



C0< -f | + C0< ' = C0( + 2H 2 



\NH 2 COOH \NH 2 X NH.CO 



Urea. Glyoxylic Urea. Allantoin. 

 acid. 



The substance crystallizes in colorless rhombic prisms, which are 

 frequently grouped in the form of stars and rosettes. It is soluble 

 with some difficulty in cold water, more readily in hot water and 

 hot alcohol, while in cold alcohol and ether it is insoluble. On pro- 

 longed boiling, it reduces Fehling's solution, and it is owing to the 

 formation of this substance, as already indicated, that uric acid can 

 reduce cupric oxide when boiled in alkaline solution (see page 256). 

 With silver, nitrate allantoin forms a crystalline precipitate of allan- 

 toin silver, if ammonia is cautiously added to the solution, but it is 

 soluble in an excess of the alkalies. 



Isolation. Allantoin is most conveniently obtained from the 

 urine of calves. To this end, the urine is evaporated on a water- 

 bath to a thick syrup and allowed to stand for several days in the 

 cold. The crystalline constituents which have formed are then 

 separated mechanically from the mother-liquor and the gelatinous 

 material which is present, and dissolved in a small amount of hot 



