1 90 DETERMINATION OF UREA IN BLOOD. [BOOK I. 



substance left on the filter is thoroughly washed with the same 

 solution and the funnel and filter are heated for some hours to 110 C. 

 At the end of that time the serum-globulin has become so insoluble 

 that it can be washed with boiling water without any risk of solu- 

 tion. It is then treated repeatedly with warm alcohol and ether, 

 dried, weighed, incinerated, and the weight of ash deducted. 



By Hammarsten's method the amount of serum-globulin found in 

 serum is sometimes greater than that of serum- albumin. (Consult 

 p. 61.) 



Determination of the presence and quantity of Urea in the Blood. 



Hoard's A weighed quantity of blood is diluted with about 



modmed to* ^ our ^ mes * ts vo ^ ume of water, acidulated with sulphuric 

 Meissner'^and acid, and boiled so as to free it from proteids. 

 Gscheidien 3 . The clear filtrate is concentrated, and treated with 



a solution of barium hydrate, which precipitates sul- 

 phates and phosphates, and the excess of baryta is removed by the 

 cautious addition of sulphuric acid. The fluid is then evaporated to 

 a syrupy consistence and mixed with absolute alcohol. The alcoholic 

 solution is separated from the precipitate (chiefly composed of inor- 

 ganic salts) which forms, the alcohol evaporated, and the residue 

 dissolved in water. The solution, which is of a light or deep yellow 

 colour, possesses an acid reaction. Solution of mercuric nitrate 

 is added cautiously ; this solution may be obtained by diluting 

 Liebig's mercurial solution for the estimation of urea with an equal 

 volume of water. A copious precipitate falls, the fluid is filtered and 

 the filtrate is rendered alkaline by adding baryta water or a solution 

 of sodium carbonate, and then more mercurial solution is added, until 

 a drop of the mixture brought in contact with solution of sodium 

 carbonate gives a yellow precipitate. 



Proceeding in this manner a white precipitate is obtained, which 

 is well washed, then diffused in water and subjected to a stream of 

 sulphuretted hydrogen, which precipitates the mercury as sulphide. 



The filtrate from the precipitate of sulphide of mercury is 



concentrated and treated with a little concentrated and perfectly 

 colourless nitric acid. After some time crystals of nitrate of urea 

 separate, which are collected on a filter, dried over sulphuric acid and 

 weighed. 



Whilst acknowledging the value of this method as demonstrating 

 the presence of urea in the blood in the most conclusive manner, 



1 J. Picard, "De la presence de 1'Ur^e dans le sang et de sa diffusion dans 

 1'organisme a I'e'tat physiologique et a l'e"tat pathologique." These de Strasbourg, 1856. 



2 Meissner, " Beitrage zur Kenntniss des Stoffwechsels im thierischen Organismus. 

 Der Ursprung des Harnstoffs im Harn der Saugethiere." Henle u. Pfeufer's 

 Zcitschrift f. rat. Medizin. Dritte Keihe. Vol. xxxi. pp. 234349. 



3 Gscheidien, Studien iiber den ' Ursprung des Harmtoffs im Thierlcorpcr. Leipzig, 

 1871. 





