PART V. RESPONSES IN PLANTS AND ANIMALS 



CHAPTER XVIII 



HOW BODY CONTROL IS BROUGHT ABOUT 



Problems : What are the chief responses to stimuli in plants and 

 animals f 



What are the means for direction and control in plants f 

 What are the means for direction and control in simple animals f 

 Hovj is man^s body controlled? 

 What are the organs of sense in man f 



Laboratory Suggestions 



Demonstration. Review of some tropisms in plants. 



Demonstration. Simple reactions in Paramecium. 



Demonstration. Some types of sensory structures, in insects, crustaceans, 

 v/orms, etc. 



Demonstration. The central nervous system of the frog compared with 

 models of the central nervous system of man. 



Demonstration. A neuron under the compound microscope. 



Home Laboratory Exercises 



(1) To determine areas of the skin most sensitive to touch. 



(2) To map out hot and cold spots on an area on the wrist. 



(3) To determine the functions of different areas on the tongue. 



Why Plants and Animals respond to Stimuli. — We have 

 learned of many instances of response to stimuli. In our experi- 

 ments with plants we have found examples of responses to Hght, 

 gravity, and moisture. These simple responses are called tropisms. 

 But if we are asked to explain why these responses took place, we 

 can only say that the protoplasm has exhibited its power of irrita- 

 bility, a power by means of which the organism is preserved from 

 injuries and by which it obtains from its environment that which 

 it needs to carry on its life processes. 



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