i GENERAL PHYSIOLOGY OF MUSCLE 67 



stimuli so frequent as to produce complete tetanus, Fick observed 

 that in the first case there was a much greater development of heat 

 than in the second. From this he concluded: 



(a) That the amount of heat developed at each contraction 

 during tetanus is in inverse ratio to the frequency of the stimuli. 



(b) That in a series of single contractions due to momentary 

 stimuli, the theriiiogenetic effect of each twitch far exceeds that 

 of each contraction of a series of such frequency as to result in 

 tetanus. 



Fick tried to express the amount of heat liberated during 

 muscular activity in absolute values. He found that the maximum 

 heat which a gram of muscle may develop during a simple con- 

 traction may reach the value of 3'1 microcalories, a microcalorie 

 being the amount of heat required to raise the temperature of 

 1 mgrm. of water 1 C. With his pupils he determined the relative 

 rates at which the development of heat and of work increased, by 

 a series of tests on frog muscle excited with maximal stimuli, and 

 loaded with regularly increasing weights. 



The general result as a rule was that the greater part of the 

 potential chemical energy liberated by the muscle during its 

 activity appeared in the form of heat. But with increase of load 

 the ratio between heat and work alters regularly, as an increasingly 

 larger part of the potential chemical energy is set free in the form 

 of work, and a comparatively smaller part as heat. This proves 

 that the muscle in doing more work functions more economically 

 than in doing little work. 



Zuntz, Lehmann, and Hagemann (1889) tried to ascertain what 

 proportion of the total energy developed in the muscles of warm- 

 blooded animals is utilised in the form of mechanical work. This 

 question has only been solved approximately by calculating the 

 total chemical energy developed by the estimation of the reciprocal 

 gas-exchanges which take place in any given work of the muscles. 

 It was shown by experiments on horses that about J of the 

 energy is transformed into work, and f into heat. If we con- 

 sider that in the best steam-engines man is able to construct 

 only jL or T V part of the energy liberated can be utilised in 

 mechanical work, all the rest being lost in the form of heat, we 

 see that the muscle is a living machine which functions more 

 economically than any steam-engine. On the other hand, an 

 electric motor fed from a battery is capable of utilising y 9 ^ 

 of the energy developed by the oxidisation of the zinc of the cell 

 in external mechanical work, so that it is a more perfect machine 

 than the muscle. We must not, however, forget that in homoio- 

 thermic animals the development of heat must not be regarded as 

 a loss, since it is as useful to the organism as mechanical work. 

 A muscle is not merely an apparatus for the production of external 

 work, but it also serves to heat the body of warm-blooded 



