THE SPINAL CORD 283 



ments in a reflex way to escape danger in the same way that a boy 

 suddenly jumps when he touches a sharp pin. 



125. To show reflex action, have a boy sit with one knee crossed 

 over the other and hanging perfectly limp. Now strike the front of 

 the knee just below the patella. The thigh muscles will contract and 

 cause the leg to kick. This will succeed best if the boy is not looking 

 when you strike. 



REVIEW TOPICS 



1. Describe the spinal cord ; its appearance and situation ; 



its gray matter, its white matter, and the origin of 

 the nerves which arise from it. 



2. Describe how the cells of the gray matter act in caus- 



ing voluntary movements, and in causing reflex 

 movements. 



3. Explain how reflex action is a protection to the body ; 



how it controls all processes of the growth and secre- 

 tion of the cells; and how it enables a person to 

 acquire skill in movements. 



4. Explain how reflex acts may be harmful; how self- 



control may overcome the harm. 



5. Describe the effects of injury to the spinal cord. 



6. Describe the effect of diseases of the spinal cord. 



