62 PHYSIOLOGY CHAP. 



Even in rest, however, muscle develops more heat than other 

 tissues. An indirect proof of this is obtained from the experi- 

 ments in which Claude Bernard attempted to estimate the oxygen 

 content of the blood flowing respectively to and from the muscle, 

 in rest and during tetanus. According to Bernard the blood of 

 the artery of the anterior rectus muscle of the dog's leg carries 

 9'31 c.c. oxygen, the blood that flows from the veins 8'21 c.c. when 

 the muscle is at rest, 3'31 during tetanus. During its activity, 

 therefore, the muscle consumes much more oxygen than during 

 rest ; but even in the resting state it consumes a certain amount, 

 and must therefore develop heat. 



These results were confirmed in Lud wig's laboratory by Meade 

 Smith (1881), who made numerous direct estimations of tempera- 

 ture, both on the blood of the artery and vein of the muscle, and 

 on the resting or tetanised muscle itself. The general conclusion 

 was that the temperature in the artery is less than in the vein 

 and in the muscle in the resting state, and that the difference 

 increases considerably during tetanus. 



Beclard was the first who studied heat production in muscle 

 from the point of view of the mechanical theory of heat (1861). 

 He tried first on the frog by the thermo-electric method, and then 

 on his own biceps muscle, to estimate with an air-thermometer, 

 graduated in fiftieths of a degree, the amount of heat developed 

 during static (isometric) contraction, in which the mechanical work 

 is nil, with that produced during dynamic (isotonic) contraction, 

 which is accompanied by mechanical work that can be measured 

 in kilogrammetres. He stated positively that when the muscular 

 contraction results in muscular work, much less heat is evolved in 

 the muscle than when a contraction of the same strength is not 

 accompanied by external mechanical effects. 



This fact, despite the imperfections of Be"clard's method, proves 

 that muscular activity is subject to the great law of the conserva- 

 tion of energy. When the whole of the energy Liberated by the 

 muscle is expressed in the form of heat, more heat is evolved than 

 when part of the energy is converted into muscular work. 



Beclard further demonstrated that the amount of energy trans- 

 formed into mechanical work during the lifting of the weight by 

 the muscle is reconverted into heat when the raising is succeeded 

 by the lowering of the weight, i.e. when the positive is followed 

 by negative work. The experiment consists in comparing the 

 heat developed when a certain weight is held up for a given time 

 by the static contraction of the biceps, with that developed during 

 the same time when the arm loaded with the same weight makes 

 up and down movements. Under these conditions (according to 

 Beclard) the development of heat indicated by the thermometer is 

 equal, whether the arm be kept in equilibrium or executes move- 

 ments. The positive work of raising the weight is therefore 



