364 THE OUTGO OF ENERGY 



Turn the drum 2 mm. again. Continue to 

 record the extension of the spring after each 

 addition of 20 grams until a load of 200 grams 

 has been reached. 



It will be found that the extension curve is a 

 straight line. The extension is directly propor- 

 tional to the weights employed. 



Eemove the weights 20 grams at a time, turn- 

 ing the drum 2 mm. after each lightening. 



The spring will return to its former length. 

 Its elasticity (within the limits of extension here 

 used) is perfect. 



Of a Rubber Band. Place the muscle clamp 

 in the stand of the heavy muscle lever (Fig. 60). 

 Secure a rubber band in the jaws of the clamp 

 and fasten the other end of the band to the 

 muscle lever. Eepeat the preceding experi- 

 ment, using 10-gram loads instead of 20-gram 

 loads. 



The extension curve will again be a straight 

 line. The return to the original length will not 

 be complete. The elasticity of the rubber band 

 is not perfect. An "extension remainder" is 

 present. After a considerable time the exten- 

 sion remainder will disappear and the band will 

 return to its former length, provided the exten- 

 sion was not too violent nor too long-continued. 



Of Skeletal Muscle. Isolate in both limbs the 



