92 



PHYSIOLOGY 



CHAP. 



variation (i.e. the current of action) which causes the transmission 

 of excitation from the nerve to the muscle, and the spread of the 

 contraction in the latter. According to d'Arsonval the thermal 

 phenomenon and mechanical work of the muscle are the effects of 

 the electrical phenomenon ; the chemical energy is transformed 



FIG. 63. Chordograms obtained by Engelmann with the apparatus described in preceding figui '<', 

 with the violin string loaded with 50 grins, and a lever that magnified fifty times. /, At a a 

 strong current was passed through the spiral for 2-3 sees. ; at b a weak current for a longer 

 time, a shows a shorter latent period, a sharper and more rapid rise, and a steeper descent 

 than b. II and ///, Uniform strength of current, but the temperature of the water was 35 C. 

 in //, 45 C. in ///. IV, After removing the water the warmth of the spiral was conveyed to 

 the string by the air which was at a temperature of 1S C. At a a stronger current was passed 

 than at b. As the cooling of the string had been accelerated, it expanded more rapidly. 

 ]', The curve falls still more rapidly, owing to accelerated cooling of the string due to a 

 stronger current of air. Time marking = 0'5 sec. 



into electrical energy, and this again into thermal and mechanical 

 energy. 



All these hypotheses are too vague and indefinite, and they 

 neglect certain well-established experimental facts. 



G. E. Miiller of Gottingen (1889) put forward a pyro-electrical 

 theory of the origin of muscular force, which, although partially 



