112-8 PHYSIOLOGY 



phenolphthalein are then added and decinormal sodium hydrate is run in until there is 

 a slight permanent pink colour. The amount of alkaline solution necessary to produce 

 this colour is a measure of the acidity of the urine. Ten cubic centimetres of formalin, 

 diluted with three volumes of water and previously neutralised to phenolphthalein 

 with decinormal alkali, are then added. The colour disappears owing to the setting 

 free of the acid radicals previously combined with ammonia. Decinormal alkali is then 

 run into the mixture until a permanent pink colour is again obtained. The number of 

 cubic centimetres of the decinormal alkali required in this second case corresponds to 

 the amount of decinormal ammonia previously present in the 25 c.c. of urine. 



This method gives somewhat higher figures than the method of Folin just described, 

 owing to the fact that the small traces of amino-acids, which may be present in the urine, 

 react to formalin in a very similar way. The difference does not exceed 10 per cent., 

 so that the method is amply delicate for clinical purposes. 



CREATININE. In Folin's method for the determination of creatinine, which is 

 now universally employed, advantage is taken of the colour reaction given by creatinine 

 (and by no other normal urinary constituent) with picric acid in alkaline solution 

 (Jaffre's reaction), the colour being compared with that of a standard potassium 

 bichromate solution. The reagents employed are decinormal potassium bichromate 

 containing 24-55 grm. per litre, saturated picric acid solution containing about 12 grm. 

 per litre, and a 10 per cent, solution of sodium hydrate. For the comparison of the 

 colours a Duboscq colorimeter is employed. 



Ten cubic centimetres of urine are measured into a 500 c.c. flask ; 15 c.c. of picric 

 acid and 5 c.c. of sodium hydrate are then added and the mixture allowed to stand for 

 five minutes. Some of the potassium bichromate solution is placed into one of the 

 cylinders of the colorimeter and its depth accurately adjusted to the 8 mm. mark. 

 At the end of five minutes the contents of the 500 c.c. flask are diluted up to 500 c.c. 

 with water and some of the mixture placed into the other cylinder of the colorimeter, 

 and the two colours are then compared. The calculation of the results is very simple. 

 If, for example, it is found that it takes 9 '5 mm. of the unknown urine picrate solution 

 to equal the 8 mm. of the bichromate, then the 10 c.c. of urine contains 



8*0 



10 x - =8-4 mg. creatinine. 

 9*5 



ESTIMATION OF URIC ACID. The best method for this purpose is a slight modi- 

 fication by Folin of the method devised by Hopkins. 

 For this method the following reagents are required : 



(1) A solution of ammonium sulphate, uranium acetate, and acetic acid, made up as 



follows : 500 grm. ammonium sulphate, 5 grm. uranium acetate, and 60 c.c. 10 per 

 cent, acetic acid are dissolved in 650 c.c. water. The volume of this solution is 

 almost exactly 1000 c.c. 



(2) Ten per cent, ammonium sulphate solution. 



(3) gQ potassium permanganate solution made by dissolving 1 -581 grm. pure potassium 

 permanganate in one litre of water ; 1 c.c. = -00375 grm. uric acid. 



Measure 200 c.c. urine with a pipette into a 500 c.c. flask and add 50 c.c of the 

 ammonium sulphate and uranium acetate reagent. Mix the solutions and allow to 

 stand for about half an hour so as to allow the precipitate to settle. This precipitate 

 contains a mucoid substance (and phosphates) which, if not thus removed, renders the 

 subsequent filtration and washing of the ammonium urate precipitate very slow. Filter 

 off the supernatant liquid through a dry filter into a dry vessel, and measure out 125 c.c. 

 ( = 100 c.c. urine) of this with pipettes into a beaker. Add 5 c.c. concentrated ammonia, 

 mix well, and allow to stand covered with paper for twelve to twenty -four hours. 



Carefully decant the supernatant liquid upon a filter, wash the precipitate of ammo- 

 nium urate on to the filter with 10 per cent, ammonium sulphate, and wash this once 

 or twice with the same reagent to remove the chlorides as completely as possible. 



Remove the filter from the funnel, open it, and with a fine stream of water wash 



