740 



LACTIC ACIDS. 



[App. 



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



C ro H 2n 3 + 2 = C n H 2re _ 2 4 + H 2 0. 



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

 the oxalic series are diatomic and diabasic. 



The following table may be given to shew the general relationships 

 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 physiology 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 sirupy, 

 colourless fluids, soluble in all proportions in water, alcohol and jether. 

 They possess an intensely sour taste, and a strong acid reaction. When 

 heated in solution they are partially distilled over in the escaping 

 vapour. They form salts with metals, of which those with the alkalis 

 are very soluble and crystallise with difficulty. The calcium and zinc 

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



1. Ethylidene-lactic acid. This is the ordinary form of the 

 acid, obtained as the characteristic product of the well-known 'lactic fer- 

 mentation.' It occurs in the contents of the stomach and intestines. 

 According to Ileintz 1 it is found also in muscles, and according to 

 Gscheidlen 2 in the ganglionic cells of the grey substance of the brain. 

 In many diseases it is found in urine, and exists to a large amount in 

 this excretion after poisoning by phosphorus 8 . 



1 Ann. d. Chem. u. Pharm. Bd. 157, S. 320. 



2 Pfluger's Archiv, 3d. vm. (187374) S. 171. 



3 Schultzen and Eiess, Ueber acute PhospJiorvcrgiftung. Chem. Ccntralb. 1869, S. 

 681. 



