120 UREA. HIPPURIC ACID. AMINOACIDS 



amount of the sulphur of the cystin fails to undergo oxida- 

 tion into sulphuric acid. In a cystinuric individual, however, 

 this latter result of administration of cholic acid does not oc- 

 cur, presumably depending upon a failure to synthesize 

 taurocholic acid. 70 An interesting addendum to these obser- 

 vations is afforded by a case of hepatic cirrhosis presenting 

 a combination of acholia and cystinuria, interpreted as an 

 instance of failure of normal taurocholic acid synthesis be- 

 cause of disease of the hepatic parenchyma, as a result of 

 which the available (for transformation into taurin) cystin 

 passed unchanged into the urine. 71 



Quantitative Determination of the Aminoacids. The 

 great number of physiological and pathological problems 

 related to the excretion of aminoacids in the urine is 

 sufficient explanation for the amount of attention devoted 

 in recent years to the elaboration of methods for the isolation 

 and estimation of these substances. For isolating the amino- 

 acids the method of binding them with naphthalinsulpho 

 chloride or with naphthylisocyanate is of service (Vol. I of 

 this series, p. 15, Chemistry of the Tissues). For estimation 

 of the aminoacid nitrogen the van Slyke method (ibid., p. 

 18), depending upon displacement of the aliphatic amino 

 group by nitric acid, 72 will be found valuable; or, too, the 

 formol-titration method of Henriques and Sorensen. The 

 latter is based on the fact that a-aminoacids in excess quanti- 

 tatively bind formaldehyde: 



/ H 



R. CH. NH a H R. CH. N = C< 



T + f = H 2 + I \H 



C O O H COH COOH. 



n E. C. Simon and D. G. J. Campbell, Johns Hopkins Hosp. Bull., 15, 365, 

 1904. 



n Observation of Morawsky, cited by J. Wohlgemuth, Deutsche Klinik, 11, 

 329, 1907. 



"P. A. Levene and D. D. van Slyke (Rockefeller Instit., New York), Jour, 

 of Biol. Chem., 12, 301, 1912. This method serves to determine not only the 

 free aminoacids, but also those combined in form of polypeptids, etc., in the 

 urine. 



