CH. XIII.] CREATININE. 337 



the case of the estimation of creatine. They give a method of purifying the 

 very doubtful specimens of wet picric acid that are at present on the market. 

 A much less troublesome method is given on p. 251, but for observations on the 

 excretion of creatine in pathological conditions it would be safer to follow Folin< 



Graham and Poulton* have shewn that the presence of aceto-acetic acid 

 in the urine inhibits the reaction with creatinine, so that the estimations are 

 too low. This acid is destroyed by the heating required for the estimation of 

 (creatinine + creatine), so that the result of the analysis always makes it 

 appear as if creatine were present. They give a method for the removal of 

 aceto-acetic acid, which must be followed when the urine gives a distinct 

 Rothera's test. They are unable to confirm the statement that creatine is 

 found in the urine as a result of carbohydrate starvation. Tt only appears 

 to be present if faulty analytical procedures are adopted, aceto-acetic acid 

 always being found in carbohydrate starvation. 



402. The estimation of creatinine (Folin).f 



Principle. A measured amount of the urine is treated with picric acid 

 and caustic soda. The picric acid is reduced to picramic acid in the cold by 

 the creatinine present, glucose having no effect in the cold (see Exs. 108 and 

 227). A known amount of creatinine is similarly treated and the solutions 

 compared in a colorimeter. 



Solutions and apparatus required. 



1. A colorimeter, see p. 384. 



2. Standard solution of creatinine zinc chloride, i -6106 gram, of the 

 pure recrystallised zinc compound (see p. 300) is dissolved in about 500 cc. of 

 distilled water and 100 cc. of Normal hydrochloric acid and the volume made 

 up to i litre with distilled water, i cc. contains i mgm. of creatinine. The 

 solution is quite stable. 



3. A saturated aqueous solution of pure picric acid (about 1-2 per cent.) 

 and a 20 cc. pipette for measuring it. 



4. 10 per cent, caustic soda, which can be measured by a pipette or 

 burette. 



5. Ostwald pipettes (fig. 48) of i cc. 



6. Two 100 cc. measuring flasks. 



Method. Into a 100 cc. measuring flask (labelled " U ") 

 measure i cc. of the urine by means of an Ostwald pipette. Add 

 20 cc. of the picric acid and then 1-5 cc. of the soda. Allow the 

 mixture to stand for 10 minutes with gentle agitation. As soon as 

 the mixture has been made measure i cc. of the standard creatinine 

 solution into the other 100 cc. flask (labelled " S "), add the picric 



* Graham and Poulton, Proc. Roy. Soc., Ixxxvii., B., p. 205. 

 f Journ. Biol. Chern., xvii., p. 470. 



