CHAPTER XIV 



MUSCULAR CONTRACTION, OXIDATION AND HEAT 

 AND LIGHT PRODUCTION 



The muscle was at one time considered to be a machine in which 

 a difference in temperature produced by oxidation is converted 

 into mechanical energy, Ibut this hypothesis does not harmonize 

 at all with the facts. A. V. Hill (1913 a) has shown that when 

 the muscle performs an isometric contraction in an atmosphere 

 of nitrogen the heat produced is about half as great as when 

 oxygen is present, and develops simultaneously with the contrac- 

 tion. Evidently this is a case, at least in part, of the transforma- 

 tion of mechanical work into heat. If oxygen is present, the 

 heat produced is much greater, but nearly half of it is produced 

 after the contraction is completed, evidently having nothing to 

 do with the contraction. 



Striated Muscle 



The muscle may work for a considerable period without oxy- 

 gen, or with the oxidations suppressed by HCN. Weizsacker 

 (1912) reduced the respiration of frog's heart to 36 per cent of the 

 normal for thirty minutes without reducing the work performed. 

 By larger doses of HCN he completely prevented the consump- 

 tion of oxygen, finding the work to be only reduced to about 

 70 per cent of the normal. This proves conclusively that the 

 muscle is not a heat machine. 



Hill measured the heat and work produced by a muscle with 

 a relatively low tension and stimulus, and found the work to 

 equal 90-100 per cent of the equivalent of the heat produced 

 during contraction. The heat produced in the relaxation period 

 was 80 per cent of that produced during contraction. Therefore 

 the efficiency of the muscle is more than 50 per cent. 



Engelmann (1893) showed that a catgut stretched in water 

 would contract on addition of acid. Stretching of the catgut 



