The spinal cord and the brain, connected with the receptors and ef- 

 fectors, regulate the adjustment of an organism to its environment; the 

 autonomic, or self-regulating system, ties all the parts together so that they 

 act as a whole through the many reflexes. 



The size and complexity of the brain are related to the ability of an 

 organism to learn, to form associations between past experience and future 

 conduct. 



Certain portions of the cerebral cortex are supposed to be involved in 

 specific sensations or movements. 



Man lives under the greatest variety of conditions, probably because he 

 is the most flexible in adjusting his natural responses and the most tenacious 

 in accumulating experiences. 



EXPLORATIONS AND PROJECTS 



1 To study reflex responses in a vertebrate, stimulate a frog gently in various 

 ways and note what responses the animal consistently makes to particular stimuli. 



To find what responses the frog makes to touch, tickle the nostril, touch the 

 eye, scratch the back gently, and stroke the back with thumb and forefinger. 

 Enumerate as many simple and consistent responses as may be observed for each 

 stimulus. 



To find the responses of the frog to chemical stimuli, use weak ammonia: 

 a matchstick moistened in ammonia. Bring it near the nostril; also touch it to 

 the frog's back. Repeat each test several times to be sure that the movements are 

 not random or accidental. (Wash the frog under running water after each appli- 

 cation.) 



To find the responses of the frog to electrical stimulation, use a two-point 

 electrical terminal connected with a 6-volt battery^ and touch the frog in several 

 places. Note the consistent responses. 



Compare the frog's responses to contact, to chemical stimulation, and to 

 electrical stimulation. 



2 To observe reflexes in human beings: 



To observe the knee jerk, have subject sit erect with the legs crossed, so that 

 the upper leg hangs limp from the knee; tap sharply just below the kneecap and 

 observe the movement that results. Note whether this movement can be con- 

 trolled. 



To observe the wink responses, have someone make a sudden motion toward 

 the subject, as if to strike the eye, and note reaction. To what extent can this 

 reaction be controlled? 



To observe the iris reflex, work in pairs: have the subject face the source of 



^Fasten the ends of two wires to the end of a glass rod by means of adhesive or friction 

 tape so that they project about a quarter of an inch and are held about a quarter of an inch 

 apart. 



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