184 Why Living Things Behave As They Do unit v 



the brain lengthwise from top to bottom. Find the cortex and the white 

 matter. Draw a single diagram of this section. 



4. Answer the following questions: {a) Is a person with a large brain 

 necessarily more intelligent than one with a small brain? Why or why 

 not? {b) What device can you think of for illustrating that the convolu- 

 tions must increase the amount of cortex in a brain? {c) Why is an injury 

 to the base of the skull particularly dangerous? {d) What would be the 

 result of destroying the part of the brain in which the nerves from the 

 eyes end? 



5. Study the diagram of the reflex arc. Draw separately {a) the re- 

 ceptor, (b) the afferent neuron, (c) the efferent neuron, and {d) the 

 effector. Make a second drawing in which you put these parts together 

 so as to make a reflex arc. When you have read further you can add neu- 

 rons to show how you become conscious of the hot stove. 



6. Are there separate receptors for "hot" and "cold" in man? Mark 

 out a one inch square on the forearm of a blindfolded student. Slightly 

 heat a needle; cool another in ice water. Using the blunt end, touch 

 nearby points within the marked area with the hot and cold needles. Put 

 a dot on a sheet of paper to correspond to the points at which warmth 

 is felt and a cross to indicate where the needle felt cold. Do the dots and 

 crosses fall on the same spots? Repeat this experiment, using other stu- 

 dents. Are the receptor maps exactly alike? 



7. In what parts of the tongue are the taste buds sensitive to substances 

 that are sour, bitter, sweet, or salt? Blindfold a student. Test various parts 

 of his tongue with sugar, salt, quinine, and lemon juice. Have him rinse 

 his mouth after each test. Record your results. Repeat with several other 

 students. Draw a diagram of the tongue and indicate the sensitivity of 

 each part to the four substances. 



8. How could you show that you smell rather than taste most sub- 

 stances? Try it and report. 



9. Do foods have the same flavor if you are blindfolded? Try it and 

 report. 



10. Are touch receptors evenly distributed over the body? Blindfold 

 a student. Your results will be better if he does not know what you are 

 going to do. Keep accurate records. Touch his forearm lightly with the 

 points of two dissecting needles or other fine-pointed instruments, the 

 points being about three eighths inch apart. Does he feel two points or one 

 point? Moving the points of the needle closer together or farther apart, 

 test various parts of the hand and forearm. For' several places find the 

 greatest distance at which he thinks the two needles are one. What was 

 the shortest distance between the points at which he could feel both? 

 What would this indicate? Now repeat the operations on the palm, 

 fingers, back of the hand, cheek, forehead, and so on. Where are touch 

 receptors closest together? Repeat the entire experiment using different 

 subjects. Why is this necessary? What are your conclusions? 



