ADVANCED PHYSIOLOGICAL CHEMISTRY 481 



The Estimation of Ammonia in Blood. Folin's Method The method 

 described on p. 468 for urine can be employed for blood with the 

 following modifications : 



1. The test-tube containing the blood must be kept on ice during 

 the estimation. 



2. Half its volume of methyl alcohol must be added to the blood 

 to prevent frothing which is apt to be excessive on account of the 

 proteids it contains. As the estimation proceeds the frothing frequently 

 becomes more marked but can be diminished by adding more alcohol. 



3. Only 5 c.c. n/10 acid and water should be placed in the absorption 

 tubes. 



4. The air current must be kept up for 5 hours. 



5. Before titrating the absorption tubes must be warmed to 30-35 C. 

 to drive oft* the C0 2 which the air current drives out of the blood and 

 which would influence the titration. 



The method depends on the fact that such ions as Ca, Mg and Na 

 (metal ions) do not produce hydrolysis of proteids and so do not 

 dislodge any ammonia, whereas they decompose the ammonia salts. 

 Hydroxyl ions, on the other hand, produce hydrolysis of proteids and 

 would give too high a result. Lime-water therefore could not be used 

 as the alkali. 



The Estimation of Sugar in Blood. To estimate sugar in blood it 

 is necessary that the proteids and haemoglobin be removed. This is 

 most easily done by Waymouth Beid's method. Into a beaker of about 

 600 c.c. capacity are placed 250 c.c. of a 7 per cent, solution of phospho- 

 tungstic acid containing 2 per cent. HC1 and the whole is weighed. The 

 blood is then added, the contents well stirred, and the beaker again 

 weighed. The difference in weight gives the amount of blood added. 

 The beaker is then heated on a sand bath (or better still an oil bath), 

 its contents being meanwhile briskly stirred. The proteids including 

 the haemoglobin are, by this treatment, precipitated and form at first 

 a brown gummy mass floating in a clear liquid. After a little the 

 coagulum becomes brittle and sinks to the bottom of the beaker. 

 Great care must now be taken that the beaker does not crack. 

 When all the coagulum has settled to the bottom, the beaker is 

 cooled and the supernatant fluid filtered through paper into an 

 evaporating dish, the paper well washed into the same dish, the 

 contents of the latter nearly neutralised with NaOH, but left faintly 

 acid, and the evaporating dish then placed on a boiling water bath. 



While the above fluid is evaporating the brittle ^roteid precipitate 

 is removed from the beaker to a mortar, ground up with some water 

 till a chocolate-like paste is obtained and then washed on to a large 



2H 



