40 



ANIMAL MECHANISM. 



its original temperature. According to our view, the sensible 

 heat has disappeared and become mechanical work. If we 

 plunge the strip when extended into water, so as to deprive it 

 of its heat, it remains, as it were, congealed in its extended 

 state, and does not develop any mechanical work. But if we 

 restore to the elongated strip the heat which it had lost, it 

 will recover its elasticity with considerable force. Fig. 9 

 represents a strip of india-rubber thus pulled out and cooled. 

 It has been laden with a weight that it may have no tendency 

 to recover itself. But, if we take the strip between our fingers, 

 we feel it swell and shorten at the same time that it lifts the 

 weight ; there is again production of mechanical work. 



If we thus heat the strip at various points we create a 

 series of lateral expansions, each of which raises a certain 

 quantity of the weight. Lastly, if we heat it throughout all 

 its extent, the strip returns to its original dimensions, with 

 the exception of the slight elongation produced by the sus- 

 pended w^eight. 



Strong analogies exist between these phenomena, and 

 those which take place in muscular tissue. The identity would 

 be perfect if the wave which heat produces on the strip of 

 india-rubber were transmitted to each end. This transference 

 implies, in the muscular fibre, the successive propagation 

 of the chemical action which disengages the heat. It is thus 

 that if we light a train of powder at one point, the in- 

 candescence spreads throughout its entire length. 



These analogies have struck us as being remarkable : they 

 seem to us to open new views of the origin of muscular 

 action. 



