376 THE OUTGO OF ENERGY 



Let the subject immediately before the stimu- 

 lus is applied forcibly contract some other group 

 of muscles ; clench the hand, for example. 



The knee jerk is reinforced. 



Ankle Jerk. Bend the foot at right angles to 

 the leg, and strike the tendo Achillis. The ex- 

 perimenter should hold the end of the foot in his 

 left hand. 



Contraction of the gastrocnemius muscle will 

 be observed. 



Gower'a Experiment. Strike the side of the 

 tendo Achillis. 



A contraction will result. 



Support the other side of the tendon so that 

 the gastrocnemius muscle will not be stretched 

 by the blow. Eepeat the experiment. 



No contraction follows. The tendon jerk re- 

 quires for its production a rapid stretching of the 

 muscles involved in the contraction. 



Try to obtain tendon jerks from other muscles ; 

 for example, the triceps humeri, flexors of hand, 

 and masseter muscles. 



"Normally no response will be obtained. 



The experiments are of value in diagnosis of 

 diseases of the central nervous system. 



