172 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



Estimation of Creatinine. 



Folin has shown that creatinine can be accurately estimated by means oi 

 Jaffe's reaction. The orange-red colour produced is matched in a colori- 

 meter against the colour of ^N solution of potassium bichromate, or better 

 against a solution of creatinine or creatinine zinc chloride which is treated 

 with the same amount of picric acid and caustic soda (see pp. 555, 562). 



The Biological Relationship of Creatine and Creatinine. 



From the chemical point of view the presence of creatinine in 

 urine would be explained by its formation from the creatine in muscle 

 by an enzyme in the animal body. An enzyme which can convert 

 creatine into creatinine has been described as being present in the liver. 

 The physiological experiments do not bear out this relationship. The 

 daily amount of creatinine in urine is constant in amount and is de- 

 rived mainly from the tissues, but very small amounts come also from 

 the food. The addition of creatine to the food does not increase the 

 amount of creatinine in urine. If the amount of creatine eaten be 

 I gm. it is not excreted as such or as creatinine ; if more than I gm. be 

 eaten, the excess over I gm. is excreted as creatine. The amount of 

 creatinine eliminated is also related to the muscular condition ; less is 

 eliminated at rest, more at work. 



Folin has suggested the following explanation : 

 Creatine is a normal constituent of the living muscle. At death 

 the muscle substance breaks down giving creatine. Normally the 

 muscle substance during its life processes gives rise to creatinine. 

 During fasting, in fevers, etc., the. normal breakdown is accompanied 

 by the breakdown into creatine. Creatine, taken as food, is absorbed 

 into the muscle and the excess is eliminated. The presence of traces 

 of creatine in urine, or of creatinine in muscle, arise chemically by the 

 action of acids or alkalies. 



