410 PHYSIOLOGICAL CHEMISTRY 



and may constitute 90 per cent or over of the total purine output. 1 

 Allantoin is formed by the oxidation of uric acid and the output is 

 increased by the feeding of thymus or pancreas to lower animals. 

 When pure it crystallizes in prisms (Fig. 131, page 409) and when impure 

 in granules and knobs. Pathologically, it has been found increased in 

 diabetes insipidus and in hysteria with convulsions (Pouchet). Mendel 

 and Dakin 2 have shown that allantoin is optically inactive notwith- 

 standing the fact that it contains an asymmetric carbon atom. This 

 phenomenon they believe to be due to tautomeric change. Wiechowski 

 has suggested an excellent method for the quantitative determination 

 of allantoin. (See Chapter XXVII.) 



EXPERIMENTS 



1. Separation from the Urine. 3 Meissner's Method. Precipitate the urine 

 with baryta water. Neutralize the filtrate carefully with dilute sulphuric acid, 

 filter immediately, and evaporate the filtrate to incipient crystallization. Com- 

 pletely precipitate this warm fluid with 95 per cent alcohol (reserve the precipi- 

 tate). Decant or filter and precipitate the solution by ether. Combine the 

 ether and alcohol precipitates and extract with cold water or hot alcohol; allan- 

 toin remains undissolved. Bring the allantoin into solution in hot water and 

 recrystallize. 



2. Preparation from Uric Acid. Dissolve 4 grams of uric acid in 100 c.c. of 

 water rendered alkaline with potassium hydroxide. Cool and carefully add 3 

 grams of potassium permanganate. Filter, immediately acidulate the filtrate 

 with acetic acid and allow it to stand in a cool place over night. Filter off the 

 crystals and wash them with water. Save the wash water and filtrate, unite 

 them and after concentrating to a small volume stand away for crystallization. 

 Now combine all the crystals and recrystallize them from hot water. Use these 

 crystals in the experiments which follow. 



3. Microscopical Examination. Examine the crystals made in the last ex- 

 periment and compare them with those shown in Fig. 131. 



4. Solubility. Test the solubility of allantoin in cold and hot water, cold and 

 hot alcohol and in ether. 



5. Reaction. Dissolve a crystal in water and test the reaction to litmus. 



6. Furfural Test (Schiff). Place a few crystals of allantoin on a test-tablet or 

 in a porcelain dish and add 1-2 drops of a concentrated aqueous solution of fur- 

 fural and 1-2 drops of concentrated hydrochloric acid. Observe the formation of 

 a yellow color which turns to a light purple if allowed to stand. This test is given 

 by urea but not by uric acid. 



7. Murexide Test. Try this test according to the directions given on page 

 397. Note that allantoin fails to respond. 



8. Reduction of Fehling's Solution. Make this test in the usual way (see 

 433) except that the boiling must be prolonged and excessive. Ultimately 



1 Wiechowski: 'JDie Purinstoffe und das Allantoin" in Neubauer and Huppert's "Ana- 

 lyse des Hams" Wiesbaden, 1913. 



2 Mendel and Dakin: Jour. Biol. Chem., 7, 153, 1910. 



* The urine of the dog after thymus, pancreas, or uric acid feeding may be employed. 



