342 



PHYSIOLOGICAL CHEMISTRY 



The lactic acid occurring in the muscular tissue of vertebrates is 

 paralactic or sarcolaclic acid, 1 



H OH 



H C C COOH. 



I I 

 H H 



The reaction of an inactive living muscle is alkaline, but upon the death 

 of the muscle, or after the continued activity of a living muscle, the 

 reaction becomes acid, due to the formation of lactic acid. There is a 

 difference of opinion regarding the origin of this lactic acid. Some 

 investigators claim it to arise from the carbohydrates of the muscle, 

 while others ascribe to it a protein origin. The strongest evidence 

 favors a carbohydrate source. 2 



FIG. no. CREATINE. 



Among the nitrogenous extractives of muscle, those which are of the 

 most interest in this connection are creatine and the purine bases, 

 xanthine and hypoxanthine. Creatine is found in varying amounts in 

 the muscles of different species, the muscles of birds having shown 

 the largest amount. It has also been found in the blood, the brain, in 

 transudates and in the thyroid gland. Creatine may be crystallized 

 and forms colorless rhombic prisms (Fig. no) which are soluble in 

 warm water and practically insoluble in alcohol and ether. Upon 

 boiling a solution of creatine with dilute hydrochloric acid it is dehydro- 

 lyzed and its anhydride creatinine is formed. The theory that the 



1 This is dextro-rotatory, whereas fermentation lactic acid (J-Wactic acid) is optically 

 inactive. 



2 Levene and Meyer: Jour. Biol. Chem., n, 361, 1912. 



