254 BODY CONTROL AND HABIT FORMATION 



Conclusion. — 1. In what respect is the frog's nervous system 

 like that of man? How does it differ? 



2. Write a description comparing the nervous system of the 

 frog with your own, using charts and models as a guide. 



Problem 223 : To study the structure and use of neurons. 



Method. — Study the figure on page 351, Civic Biology. The 

 cell pictured is known as a neuron or a unit of the nervous system. 

 The brain and spinal cord contain many millions of them. One 

 end of a neuron may be in the brain and the other end far away 

 in the spinal cord ; or one end may be near the surface of the 

 body and the other end in the spinal cord or brain. 



Observations. — How do these cells compare in length with 

 other cells of the body ? 



NOTE. — If a neuron has for its function the sending of messages from within 

 outwards (to muscles), it is a motor nerve. If it receives stimuli from without, it ia 

 a sensory nerve. 



Conclusion. — AVhat structures in the nervous system carry 

 the impulses from the surface to the brain? From the brain 

 to the muscles or other parts of the body? 



Problem 224 : What is a reflex action ? 



Method and Observations. — If somebody, without warning, 

 pretends to strike you in the face, what happens? Through 

 . what parts of the nervous system would you become aware of 

 what was happening? 



With your eyes closed touch a hot surface. What happens? 

 Did you think about withdrawing your hand? 



Conclusion. — 1. Actions of the sort just described are called 

 reflexes. Explain as well as you can, using the figure, the path- 

 way of a reflex action. 



2. Does this pathway reach the cerebrum or thinking part of 

 the brain? 



Problem, 225 : To compare the reaction time of hearing and 

 touch. 



Method and Observations. — Let the class form a large circle 

 and then start a whispered word at one end of the circle. Let the 



