no THE MECHANISM OF LIFE 



The fourth state of muscular contraction is when the 

 muscle is doing negative work, i.e. when work is being done 

 on it, as for instance when we go downstairs, or when a 

 descending weight forces down the opposing arm which 

 attempts to support it. In this case the muscles receive a 

 portion of the energy lost by the descending weight, and this 

 energy shows itself in the muscle in the form of heat. This 

 increase of heat in a muscle doing negative work has been 

 clearly demonstrated bv the calorimetric experiments of Hirn 

 and the thermometric experiments of Beclard. Hirnfe ob- 

 servations on muscular calorimetry show a production of heat 

 corresponding to 150 calories per hour when in repose, 

 °.48 calories per hour during positive work, and ScST during 

 nee-ative work. Beclard's thermometric measurements also 

 show that the temperature of a muscle rises each time that it 

 contracts, and that the rise of temperature is greatest when 

 the muscle is doing negative work, least during positive work, 

 and intermediate when in a state of tension. 



It is of the greatest importance in medical practice to 

 distinguish between these different forms of muscular activity. 

 There is a vast physiological difference between muscular 

 contraction with the production of positive work, and muscular 

 contraction without the production of work, or with negative 

 work. To climb a flight of stairs is to contract the muscles 

 with the production of work equal to the weight of the body 

 multiplied bv the height of the stairs. To descend the stairs 

 is to contract the same muscles, but with the production of 

 negative work, and consequently a maximum of heat. To 

 walk on level ground is to contract the muscles with the 

 production of little or no external work ; as in a machine 

 turning without friction in a vacuum. 



We have seen that a fall of potential and a current of energy 

 are the necessary conditions f r the [ reduction of any natural 

 phenomenon. Hence we may assume that the phenomenon 

 of sensation is also accompanied by a fall of potential and a 

 current of energy. When we touch a hot body, there is a How 

 of energy from the hot body to l.:c hand. When we touch a 

 cold body, there is a current of energy in the opposite direction, 



