222 NERVOUS REACTIONS 



activity. There will then be attending respiratory, circulatory, 

 and glandular activities. For example, a rabbit sees a cat and 

 tries to escape. The sensory stimulus is the sight of the cat while 

 the reaction is the motor act of escaping. Because fear attends 

 this voluntarv act, the autonomic centers of the rabbit are stim- 

 ulated and their resulting activities favor the response of out- 

 witting the cat. The bronchial tubes of the frightened rabbit are 

 relaxed and rapid breathing is made easier. The contraction of 

 blood vessels in the viscera and the increased heart action forces 

 more blood into the skeletal muscles. Thus, extra oxygen and 

 fuel are supplied to the muscles. The nerves stimulate the 

 adrenal glands which pour out their secretion into the blood, 

 causing the liver to give up more sugar into the blood, as well as 

 increasing the endurance and strength of the muscles and reducing 

 the activities of digestion. The rabbit has more energ}^ than 

 normallv and is able to run faster from the cat which is activated 

 purely by the instinct of hunting. But, if the cat is aroused by 

 a strong feeling of hunger, we would find in her activities very 

 similar to those in the rabbit. In this case, the probability of 

 escape by the rabbit would be lessened. 



The nature of the nerve impulse. The nature of the nerve 

 impulse is not fully understood. The speed with which it travels 

 along a motor nerve fiber is about three hundred and ninety feet 

 per second. The time elapsing between the application of a 

 stimulus and the response varies in different individuals and in 

 the same individual under different conditions. It depends upon 

 the strength of the stimulus. If the stimulus is very strong the 

 response will be prompt. If the stimulus is weak the response 

 is not made or is made very slowly. The time of reacting is 

 dependent upon the nature of the stimulus. For example, the 

 response to a person walking toward you is quite different from 

 the response given when an automobile comes toward you. The 

 time is also aft'ected by the number of synapses through which the 



