PROTEIC ACID FRACTION 139 



The alloxyproteic acid fraction apparently contains at 

 times four substances: Dombrowski's urochrome (recogniz- 

 able by its precipitation by neutral lead acetate and by 

 copper acetate, and the insolubility of its lead salt in dilute 

 acetic acid), true urochrome of Weiss and the colorless allo- 

 xyproteic acid of the Polish writers True urochrome, the 

 normal yellow coloring matter of urine, is not the same as 

 Dombrowski's urochrome, and may be differentiated from 

 the latter by the solubility of its lead salt in dilute acetic acid. 

 In addition urochromogen, occurring in pathological urines, 

 is found for the most part in this fraction (careful precipita- 

 tion avoiding excess of lead acetate) ; but sometimes, it is 

 true, it is met in the autoxyproteic acid fraction. 



Weiss 56 has devised a method by which it is possible to 

 estimate by comparative colorimetry the amount of 

 urochrome and urochromogen in a urine with great exact- 

 ness. The urine is first freed of other coloring materials by 

 saturation with ammonium sulphate (urobilin, haematopor- 

 phyrin and uroerythrin) ; and the color of the filtrate is then 

 compared by means of a Dubosq colorimeter with a true 

 yellow solution of known content. If urochromogen is pres- 

 ent along with urochrome a dilute solution of permanganate 

 is cautiously added as long as increase in the yellow color 

 can be clearly recognized or until the Ehrlich's diazo-reac- 

 tion, if at first present, begins to fail ; thereafter the process 

 is as above. The difference between the quantities of uro- 

 chrome obtained before and after the full oxidation repre- 

 sents the quantity of urochromogen present in the specimen. 

 In examining urines with positive diazo-reactions there is 

 always to be noted a direct proportion between the intensity 

 of the diazo-reaction and the amount of urochromogen in the 

 urine. The technical simplicity and the sensitiveness of the 

 urochromogen reaction with permanganate makes it possible 

 to substitute the diazo-reaction by the former. 



58 M. Weiss, Biochem. Zeitschr., SO, 345, 1911. 



