346 THE OUTGO OF ENERGY 



TETANUS 



Superposition of Two Contractions. Arrange 

 a gastrocnemius muscle to write on a smoked 

 drum. Connect the binding posts on the muscle 

 lever and muscle clamp with the secondary coil 

 of an inductorium. In the primary circuit (posts 

 1 and 2) place the electro-magnetic signal and a 

 simple key. Let the drum revolve at a rapid 

 rate. Send two maximal induction currents 

 through the muscle at varying intervals, begin- 

 ning with the shortest interval possible. The 

 secondary should be at such a distance from 

 the primary coil that both make and break cur- 

 rents shall cause maximal contraction. 



If the second stimulus fall in the latent period 

 of the first contraction, the stimulus will be with- 

 out effect. If the second stimulus fall between 

 the beginning of shortening and the end of relax- 

 ation caused by the first stimulus, the contraction 

 following the second stimulus will not begin from 

 the base line, but will be superposed on the first, 

 as if the state of shortening from which the 

 second contraction begins were the resting stage 

 of the muscle. The height reached by the 

 second contraction will be greater than that 

 reached by the first. The summed height is 



