CHEMICAL BASIS OF THE ANIMAL BODY. 



891 



By further oxidation a member of the glycolic series can be converted into a 

 member of the oxalic series. Thus : 



. Glycolic acid. Oxalic acid. 



C 2 H 4 O 3 + 2 = C 2 H 2 4 + H 2 0, or more generally 

 C n H 2w 3 + 2 = C n H 2n - 2 4 + H 2 0. 



The acids of the glycolic series are diatomic but monobasic; but those of the 

 oxalic series are diatomic and dibasic. 



The following table may be given to show the general rejationship of alcohols 

 and acids : 



GLYCOLIC ACID SERIES. 

 Lactic Acid. C 3 H 6 3 . 



Next to carbonic acid, the most important member of this series, as far as physi- 

 ology is concerned, is lactic acid. 



Lactic acid exists in four isomeric modifications, but of these only three have 

 been found in the human body. These three all form syrupy, colorless fluids, solu- 

 ble in all proportions in water, alcohol, and ether. They possess an intensely sour 

 taste, and a strong acid reaction. When heated in solution they are partially dis- 

 tilled over in the escaping vapor. They form salts with metals, of which those 

 with the alkalies are very soluble and crystallize with difficulty. The calcium and 

 zinc salts are of the greatest importance, as will be seen later on. 



1. Ethyli dene-lactic acid. This is the ordinary form of the acid, obtained as 

 the characteristic product of the well-known kt lactic fermentation." It occurs in 

 the contents of the stomach and intestines. According to Heintz. 1 it is found also 

 in muscles, and according to Gscheidlen 2 in the ganglionic cells of the gray sub- 

 stance of the brain. In many diseases it is found in urine, and exists in a large 

 amount in this excretion after poisoning by phosphorus. 3 



It may be prepared by the general methods of slowly oxidizing the corresponding glycol or by 

 acting on monochlorinated propionic acid with moist silver oxide. In obtaining it from the pro- 

 ducts 9f lactic fermentation, the crusts of zinc lactate are purified by several crystallizations, and 

 the acid liberated from the compounds 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. 4 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. 



Wislicenus first obtained this acid by heating hydroxycvanide of ethylene with aqueous solu- 

 tions of the alkalies. 



The same observer found it also in many pathological fluids. 



3. Sarcolactic acid. This acid has not yet been procured synthetically. As 

 its name implies, it is that form of the acid which chiefly occurs in muscles, and 



1 Ann. d. Chem. u. Pharm., Bd. clvii., S. 320. 



'> Pflxiger's Archiv. Bd. viii. (1873-74), S. 171. 



3 Schultzen and Riess, Ueber acute Phosphorvergiftung. 



* Ann. d. Chem. u. Pharm.. Bd. cxxviii., S. 6. 



Chem. Centralb., 1869, 8. 681. 



