102 DETERMINATION OF UREA IN BLOOD. [BOOK I. 



nitrogenous proximate principles than urea evolve nitrogen under 

 these circumstances, it is unphilosophical and inaccurate to consider 

 the nitrogen as all derived from urea. There is doubtless much 

 force in this objection; nevertheless as unquestionably urea is 



FIG. 38. DUPRE'S APPARATUS. 



infinitely the most abundant of the nitrogenous extractive matters 

 of the urine and of the blood, and as it is the only body which 

 does yield nearly the whole of its nitrogen to hypobromite, the 

 estimate of urea based upon nitrogen evolved under these cir- 

 cumstances is very near the truth. The method is one, too, 

 which yields most concordant results. 



Haycraft's This method, which was worked out by John Hay- 



method 1 , craft, M.B., in Professor Ludwig's Laboratory, appears 



to be likely to supersede all others, though it has not yet been 



1 Communicated privately to the Author. A short account of this method has 

 already appeared in the Journ. f. pract. Chemie. 



