124 



ESSENTIALS OF CHEMICAL PHYSIOLOGY 



in the laboratory ; the equation which represents the formation of urea 

 from creatine is as follows : — 



C4H9N3O2 + H20=C3HvN02 + CON2H4 



[creatine] [water] [sarcosine] [urea] 



The second substance formed is sarcosine. Sarcosine is methyl-glyco- 

 cine — that is, amido-acetic acid in which one H is replaced by methyl 

 (CH3) 



pTT /NH.CH3 



u±i2S.(^Q0H 



It is, however, doubtful whether decompositions of this kind occur 

 in the body (see p. 113). 



With sodium nitro-prusside creatinine gives a colour reaction 

 described on p. 106. 



Creatinine with zinc chloride gives a characteristic crystalline 

 precipitate (groups of fine needles) with composition C4H7N30.ZnCl2. 



According to the recent researches of G. S. Johnson, urinary 

 creatinine, though isomeric with the creatinine obtained artificially 



Fig. 45. — Creatine crystals. 



Fig. 46. — Creatinine crystals. 



from the creatine of flesh, differs from it in some of its properties, 

 such as reducing power, solubility, and character of its gold salts. 

 The reducing action of urinary creatinine has led to some confusion, 

 for some physiologists have supposed that the reducing actio n on 

 Fe bling's solution a nd picric acid of normal urine is due to sugar, 

 whereas it is really chiefl y due to creatinine. The readiest way of 

 separating creatinme from urine is the following : — To the urine a 

 twentieth of its volume of a saturated solution of sodium acetate is 

 added, and then one-fourth of its volume of a saturated solution of 

 mercuric chloride : this produces an immediate abundant precipitate 



