34 2 PHYSIOLOGICAL CHEMISTRY. 



shows, at least, the possibility of such a formation. The 

 amount of lactic acid formed in the muscle seems to be great- 

 est during working periods, which is true also of the final 

 products of katabolism. The acid may simply represent a 

 stage in the gradual breaking down, whether we consider a 

 carbohydrate or protein as the parent substance. We should 

 expect therefore an increase in the muscle acid if the oxida- 

 tion processes of the body are hindered or retarded, while at 

 the same time protein or sugar decomposition is increased, 

 or, at any rate, not diminished. In the dead muscle the en- 

 zymic formation of lactic acid doubtless continues long after 

 the oxidation reaction ceases, and this is probably the main 

 reason for the ready detection in the muscle after death. 



The pure acid occurs as a thickish liquid miscible with 

 water. It forms salts which are mostly readily soluble. The 

 zinc and calcium salts crystallize well and are hence prepared 

 for identification. The pure liquid shows a right hand optical 

 rotation, with [a] D = about 3. The result is not constant 

 because of the difficulty of preparing concentrated solutions 

 free from anhydride or lactide. The rotation of the salts, on 

 the contrary, is to the left. 



The Inorganic Salts. Although making up not much 

 over i per cent of the weight of the moist muscle, these salts 

 are extremely important. Of dry substance the salts consti- 

 tute 5 per cent or more. The salts are usually estimated from 

 the ash left in burning the muscle; this gives of course no 

 correct idea of how they are combined in the living muscle, 

 but is the only method available. In the living muscle many 

 of the inorganic elements are doubtless in chemical union with 

 proteins or other organic groups, while in the derived ash we 

 have chlorides, phosphates, sulphates or carbonates. A car- 

 bonate is probably formed during the combustion of organic 

 acids and corresponds to no simple preexisting compound. 

 Phosphorus and sulphur of proteins furnish phosphates and 

 sulphates. The analyses of ash made disclose very different 

 results, but mean values may be given to show the general 



