180 THE CHEMISTRY OF SOME FOODS. [CH. VII. 



The purine bases found in meat extracts are chiefly 

 hypoxanthine and xanthine. They can be obtained from 

 the alcoholic solution obtained in Ex. 166, by evaporating 

 off the alcohol, adding ammonia and precipitating with 

 ammoniacal silver nitrate. 



Sarcolactic acid is ctoro-a-hydroxy-propionic acid. 



OH 



CH 3 .CH.COOH. 



The lactic acid found in muscle is d-lactic. That 

 formed by the fermentation of lactose and other carbo- 

 hydrates is generally ^/-lactic. Certain bacteria, however, 

 produce /-lactic acid (see p. 151). 



Sarcolactic acid is present to a very small extent in 

 fresh living muscle. The amount increases rapidly in 

 fatigue, especially in the absence of a proper supply of 

 oxygen. On leaving a fatigued muscle in an atmosphere 

 of oxygen, the amount of lactic acid decreases. 



There is a considerable production of lactic acid at the 

 onset of rigor mortis. But if a fresh muscle be suddenly 

 coagulated by dropping it into boiling water, there is no 

 such marked production of the acid. 



It is probable that the lactic acid appearing in fatigue 

 and in rigor arises through the decomposition of some 

 carbohydrate material in the muscle, but this has not been 

 definitely established. 



Sarcolactic acid is a liquid, soluble in water, alcohol 

 and ether. It forms a characteristic zinc salt, which is 

 obtained by boiling a solution with excess of zinc carbonate, 

 filtering and evaporating slowly. The crystals contain 

 two molecules of water of crystallisation, the zinc salt of 

 ordinary fermentation lactic acid containing three. 



229. Hopkins' reaction for lactic acid. To 3 drops of 

 a i per cent, alcoholic solution of lactic acid in a clean, dry test 

 tube add 5 cc. of concentrated sulphuric acid and 3 drops of a 





