76 ORGANIC FUNCTIONING 



of events is repeated. Ultimately the muscle-fibre will refuse 

 to respond unless the supply of carbohydrate and oxygen are 

 renewed. 



25^. Oxidation in the Muscle- Fibre. As the fibre 

 continues to contract lactic acid accumulates in it. But the 

 fibre continually receives oxygen from the blood and thus {via 

 the agencies of oxidases — see Section 28^) the lactic acid is 

 converted into CO 2 and OH 2. These latter substances are 

 removed in the venous blood and eliminated from the body. 

 But in the oxidation of lactic acid available energy is produced 

 (for that of CO 2 and OH 2 is much less than that of lactic acid). 

 Some of this energy coming from the oxidation of lactic acid 

 restores that part of the carbohydrate that has supplied the 

 energy of tension to its original reactive state. The rest of 

 the energy of the oxidation transforms into heat. Ultimately, 

 of course, the quantity of carbohydrate decreases and must be 

 renewed. 



25^. The Contractile Muscle- Fibre is not a Thermo- 

 dynamic Mechanism. A steam, or internal-combustion engine 

 is a thermodynamic mechanism. In the former heat enters the 

 cylinders, expands the steam and actuates the engine. Heat 

 leaves the engine via the condenser water. More heat enters the 

 engine in the steam than leaves it in the condenser water and the 

 balance of heat energy transforms into the kinetic energy of the 

 moving parts of the engine. There are two temperatures : T2, 

 which is that of the steam and Ti which is that of the condenser 

 water and T2>Ti. The greater is the difference T2 — Ti, 

 the greater is the efficiency of the engine (so an internal-combus- 

 tion engine is more efficient than a steam-engine). 



But if there is any such temperature- diff"erence between the 

 muscle which is more tense and that which is less tense it must 

 be very small and so the muscle mechanism must be very in- 

 efficient — if it is a thermodynamic mechanism. But the muscle 

 mechanism is highly efficient and therefore it cannot be a thermo- 

 dynamic mechanism. 



25/. The Motive Force of Muscular Activity depends 

 ultimately on the Oxidation of Carbohydrate Material. 

 This must be obvious since the muscle carbohydrate disintegrates 

 partially into lactic acid and the latter is removed by oxidation. 

 The muscle supply of carbohydrate diminishes and must be 



