286 



PHYSIOLOGICAL CHEMISTRY. 



that allantom is a constant constituent of the urine of such animals. 

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

 increased by thymus or pancreas feeding. When pure it crystal- 

 lizes in prisms (Fig. 93, below) and when impure in granules and 



FIG. 93. 



ALLANTOIN, FROM CAT'S URINE. 



a and b, Forms in which it crystallized from the urine ; c, re-crystallized allantoin. 

 (Drawn from micro-photographs furnished by Prof. Lafayette B. Mendel of Yale 

 University.) 



knobs. Pathologically, it has been found increased in diabetes 

 insipidus and in hysteria with convulsions (Pouchet). 



EXPERIMENTS. 



1. Separation from the Urine. 1 Meissner's Method. Precipi- 

 tate the urine with baryta water. Neutralize the filtrate carefully 

 with dilute sulphuric acid, filter immediately and evaporate the fil- 

 trate to incipient crystallization. Completely precipitate this warm 

 fluid with 95 per cent alcohol (reserve the precipitate). Decant or 

 filter and precipitate the solution by ether. Combine the ether and 

 alcohol precipitates and extract with cold water or hot alcohol; 

 allantom remains undissolved. Bring the allantoin into solution in 

 hot water and recrystallize. 



Allantom may be determined quantitatively by the Paduschka- 

 Underhill-Kleiner method (see p. 407) or by Loewi's method. 2 



2. Preparation from Uric Acid. Dissolve 4 grams of uric 



1 The urine of the dog after thymus, pancreas or uric acid feeding may be 

 employed. 



2 Archiv f iir Experimentelle Pathologic und Pharmakologie, 1900, xliv, p. 20. 



