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 is 

 a sensory nerve. 



Conclusion. — What 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 reflejc 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 



