46 CONTRACTILITY 



The former method depends upon the fact that if a 

 circuit be formed of two different metals, any difference of 

 temperature between the two junctions will cause a current 

 to pass through the circuit. One junction is placed upon 

 the muscle which is to undergo contraction, the other upon 

 a muscle which remains inactive. The current is detected 

 by a galvanometer. 



The bearing of the results obtained by these methods 

 upon the mechanical efficiency of muscle and upon the 

 nature of muscular contraction will be dealt with later. For 

 the moment it is only necessary to state the important 

 fact that the energy of tension varies directly with the length 

 of the tmiscle before it contracts. 



THE NATURE OF CONTRACTION 



Since all tissue activity is the result of oxidation, we may 

 study the effect of oxygen upon contraction. In the 

 presence of oxygen there is a utilisation of carbohydrate 

 and of oxygen, and evolution of COg. In absence of oxygen, 

 contraction occurs as before and carbohydrate is utiUsed, 

 but the outstanding chemical change is the accumulation, 

 of lactic acid. There is no evolution of CO2 other than can 

 be explained as produced secondarily by the action of the 

 lactic acid upon the bicarbonates present. 



Under these conditions, however, the muscle soon becomes 

 fatigued, recovery ensuing on the administration of oxygen. 



Oxygen therefore, while essential for the continued 

 activity and well-being of the muscle, is not necessary for 

 the actual contractile process. Nor is anaerobic contraction 

 due to the consumption of a kind of intramuscular store 

 of oxygen, otherwise there would be a considerable evolution 

 of COg. The act of contraction, therefore, is associated 

 chemically not with an oxidative process but with the 

 formation of lactic acid. The uncontracted muscle con- 

 tains within it a store of potential energy which in the 

 assumption of the contracted state is capable of transforma- 



