METHOD OF ESTIMATING ALLANTOIN 169 



the urine with hydrochloric acid, inoculating it with a bit of 

 uric acid and subsequently shaking the urine for a long time 

 when the salt-like combined uric acid is separated, presum- 

 ably completely. However, this method furnishes distinctly 

 lower results than the Ludwig-Salkowski and other methods, 

 probably because it leaves complex uric acid combinations 

 intact. It may, however, possibly serve, if more fully elab- 

 orated, to separate the uric acid which is in the blood in loose 

 salt-like form from that in firmer combination. 64 



Wiechowski's Method of Estimating Allantoin. Befer- 

 ence has been made to the very great importance of 

 Wiechowski's method of determining allantoin, and the 

 statement made that the introduction of this method, which 

 had been worked out very precisely, had determined the turn- 

 ing point in the historical development of the study of purin 

 metabolism. The method consists first of removal of all 

 substances from the urine which can be precipitated by 

 means of phosphotungstic acid, acetate of lead and acetate 

 of silver, after which the allantoin is thrown down by 

 mercuric acetate with addition of sodium acetate after care- 

 ful neutralization. In animal urine the nitrogen content of 

 the precipitate may then be directly determined ; the impuri- 

 ties in the precipitate being in such small amount that they 

 are scarcely appreciable analytically in proportion to the 

 relatively large amount of allantoin. However, in case of 

 the very scant quantities of allantoin in human urine, the 

 conditions are quite different. In this case simple nitrogen 

 determination of the precipitate cannot be used, and it is 

 essential to have recourse to purifying processes to enable 

 us to separate and weigh the allantoin in crystalline form. 65 



"A. Nicolaier and M. Dohrn, Deutsch. Arch. f. klin. Med., 91, 151, 1907; 

 B. Bloch (Med. Clinic of W. His, Basel), Deutsch. Arch. f. klin. Med., 83, 499, 

 1905 ; Meisenburg, ibid., 87, 425, 1906. 



W W. Wiechowski, Hofmeister's Beitr., 11, 121-131, 1907; Biochem. 

 Zeitschr., 25, 446-453, 1910. 



