APR] CHEMICAL BASIS OF THE ANIMAL BODY. 741 



It may be prepared by the general methods of slowly oxidising the corresponding 

 glycol or by acting on monochlorinated propionic acid with moist silver oxide. 

 In obtaining it from the products of lactic fermentation, the crusts of zinc lactate 

 are purified by several crystallisations, and the acid liberated from the compound by 

 the action of sulphuretted hydrogen. 



2. Ethylene-lactic acid. This acid is found accompanying the 

 next to be described, in the watery extract of muscles. From this it is 

 separated by taking advantage of the different solubilities in alcohol 

 of the zinc salts of the two acids. It seems probable, however, that 

 it has not yet been prepared in the pure state by this method. 



TVislicenus first obtained this acid by heating hydroxycyanide of ethylene with 

 aqueous solutions of the alkalis 1 . 



The same observer found it also in many pathological fluids. 



3. Sarcolactic acid. This acid has not yet been procured syn- 

 thetically. As its name implies, it is that form of the acid which 

 chiefly occurs in muscles, and hence exists in large quantities in Liebig's 

 ' extract of meat.' It is often found also in pathological fluids. This 

 is the only acid of the series which possesses any power of rotating the 

 plane of polarised light; it is otherwise indistinguishable from the 

 preceding ethylidene-lactic acid, and is generally represented by the 

 same formula. The free acid has dextro-, the anhydride Isevo-rotatory 

 action. The specific rotation for the zinc salt in solution is -7' 65 for 

 yellow light. 



The zinc and calcium salts of sarcolactic acid are more soluble both 

 in water and alcohol, than those of ethylidene-lactic acid, but less so 

 than those of ethylene-lactic acid, and the same salts of ethylene-lactic 

 acid contain more water of crystallisation than those of the other two. 



Heintz 2 has compared the above acids to the modifications capable of existing in 

 tartaric acid 3 . 



Hydracrylic acid, the fourth in this series of lactic acids, is distinguished by the 

 nature of its decomposition on heating. It is never found as a constituent of 

 animal bodies. 



OXALIC ACID SERIES. 



Oxalic acid. H 2 C 2 O 4 . 



In the free state this acid does not occur in the human body. Cal- 

 cic oxalate, however, is a not unfrequent constituent of urine, and 

 enters into the composition of many urinary calculi, the so-called mul- 

 berry calculus consisting almost entirely of it. It may occur in fseces, 

 and in the gall bladder, though this is rarely observed. 



1 Ann. d. Chem, u. Pharm. Bd. 128, S. 6. 



2 Op. cit. 



3 See further, Wislicenus, op. cit. Also Ann. d. Chem. u. Pharm. Bd. 166, S. 3, 

 Bd. 167, S. 302, and Zeitschr. f. Chem. Bd. xm. S. 159. 



