THERMAL AND CHEMICAL CHANGES IN MU8CLE of)? 



2. The Chemical Changes induced by Activity. Tne methods used 

 for investigating tissue respiration show that an increased amount of 

 oxygen is used up, and more C0 2 formed, when muscle is contracting 

 than when at rest. If the hind-limb of a frog be tetanized, it will be 

 found the plasma expressed from the muscles gives the colour reactions 

 for lactic acid. The muscles of the resting limb give no such reactions. 

 If the limb be made to contract in an atmosphere of oxygen, no 

 lactic acid is formed, for it is only when the muscle is made to con- 

 tract with an insufficient supply of oxygen that this acid is formed. 

 Such is the case in man during excessive, muscular exercise. The 

 lactic acid then formed can be shown in the urine and in the sweat. 

 In the blood it plays an important part in the production of the 

 dyspnoea attendant upon such exercise. 



It has been suggested that lactic acid might come from muscle 

 protein or from the complicated body known as " phosphocarnic acid." 

 However, researches into the amount of nitrogen and sulphur excreted 

 in the urine at rest and after muscular exercise tend to show that the 

 protein metabolism is not greatly affected by muscular exercise 

 certainly not in sufficient amount to account for the tactic acid 

 formation. 



Dextrose is apparently the chief source of the lactic acid. 



C 6 H ]2 O 6 = 2C 3 H 6 3 



Daxtrose Lactic acid 



When ample oxygen is present. C0 2 and water are formed as the 

 waste products of contraction and any lactic acid that appears in 

 the process is rebuilt into the muscle substance. 



C 6 H 12 6 + 6O 2 = 6CO, + 6H,0. 



-The exact significance of the creatin and hypoxanthin present in 

 muscle is not known. Tney do not appear to be waste products. It 

 is possible that the muscle may perform some of its work at the expense 

 of these bodies, especially the hypoxanthin, since muscular exercise 

 after a delay is followed by an increased excretion of uric acid in the 

 urine. Further, meat extracts have a restorative, effect upon muscle 

 tone. 



3. Rigor Mortis. When a muscle dies, either as a result of its 

 removal from the body or by reason of general bodily death, it 

 (1) loses its transparency, and becomes opaque; (2) shortens; (3) 

 develops an acid reaction, and evolves carbon dioxide; (4) passers from 

 a semifluid to a firm, solid state, or rigor. 



After death, this rigor supervenes in a more or less definite order 

 first the jaws, then neck, trunk, upper and lower limbs. The rate 

 of onset varies. Generally, several hours elapse; but if just previous 

 to death the muscles have been greatly fatigued, particularly in the 

 absence of oxygen, the changes may set in at once. Soldier.; are said 

 to have been found standing dead in the trenches, with the rifle held 

 to the shoulder, probably due to shell -burst and oxygen deprivation 

 by carbon monoxide. After a time generally two to six daye this 



