370 THE OUTGO OF ENERGY 



IV 



THE CENTRAL NERVOUS SYSTEM 

 SIMPLE EEFLEX ACTIONS 



The Spinal Cord a Seat of Simple Reflexes. 



1. By means of a hook or thread passed through 

 the lower jaw suspend vertically a frog the brain 

 of which has been destroyed with the seeker ; the 

 legs must not touch the table. Pinch a toe with 

 the forceps. 



The leg will be drawn up. 



A stimulus to the skin has caused the con- 

 traction of muscles. The afferent impulse set 

 going by the sensory stimulus is changed into 

 a motor efferent impulse. This is an example of 

 reflex action. 



2. Destroy the spinal cord with the seeker. 

 Stimulate the skin of the right leg electrically 

 and mechanically. 



In no case will the sensory stimulus call forth 

 the reflex contraction of a skeletal muscle. Yet 

 the nerves coming from the skin and going 



