454 PRACTICAL PHYSIOLOGY 



separated from the urine by adding a solution of lead acetate, filtering 

 off the precipitate of inorganic salts which at first forms and allowing 

 the filtrate to stand, when large needle-shaped glancing crystals of 

 the lead salt separate out. If these be collected and treated with 

 sulphuretted hydrogen, so as to remove the lead, the acid is obtained 

 in a pure state. 



Glycuronic Acid. Chemically this is dextrose in which the end 

 CH 2 OH group has become oxidised to form COOH, or carboxyl. It 

 has, accordingly, the formula COOH (CH.OH) 4 CHO. It is an 

 intermediate body in the metabolism of dextrose, and usually becomes 

 further decomposed in the organism, to yield carbon dioxide and 

 water. Sometimes, however, it unites with the aromatic bodies 

 (plenol, skatol, etc.) absorbed from the intestine to form a salt. In 

 this combination it takes the place of sulphuric acid (see p. 435). In 

 very small amount, it seems to be always present in the urine, but 

 under certain conditions (as after the administration of certain drugs) 

 it becomes increased to such an extent as to impart to the urine a 

 very considerable power of reducing metallic oxides in alkaline 

 solution. When this is the case it is apt to be confused with dextrose. 

 The only absolute test whereby it may be distinguished from dextrose 

 is that it does not ferment with yeast. It gives the pentose reactions. 



CHAPTER XXI. 

 LACTIC ACID, ITS ESTIMATION AND SIGNIFICANCE. 



By J. H. RYFFEL, M.A., B.Sc., Demonstrator of Physiology, Guy's 



Hospital. 



THE lactic acid of the body, called sarcolactic acid, is the dextrorotatory 

 variety, the free acid rotating the plane of polarisation of polarised 

 light to the right, while its metallic salts rotate to the left. The 

 specific rotatory power of the zinc salt [a] B (see p. 354) is - 7'5 

 to - 6 5 according to the strength of the solution. The zinc salt 

 contains two molecules of water of crystallisation, whilst that of the 

 inactive or fermentation lactic acid contains three molecules. 



Identification and Estimation of Lactic Acid. Ether Extraction 

 Method, If the material is blood or tissue, it is extracted with alcohol or 

 with boiling water; if urine, it is concentrated and extracted with alcohol. 



