THE NERVOUS SYSTEM. 175 



whenever improper substances enter the air-passages. 

 Winking is an act of the same sort, and serves both to 

 shield the eyes from too great glare of light, and to pre- 

 serve them by keeping the cornea moist. Looking at the 

 am or other strong light, causes sneezing by reflex action. 

 Laughing, whether caused by tickling the feet or by some 

 happy thought, and also sobbing, are reflex acts, taking 

 place by means of the respiratory muscles. 



60. Certain of the protective reflex movements call into 

 play a large number of muscles, as in the balancing of the 

 body when walking along a narrow ledge, or on a slippery 

 pavement. The dodging motion of the recruit, when the 

 first cannon ball passes over his head, is reflex -and invol- 

 untary. The fact that these involuntary, reflex acts are 

 performed with great precision, will explain why it is that 

 accidents seldom befall the somnambulist, or sleep-walker, 

 although he often ventures in most perilous places. 



61. Walking, sitting, and other acts of daily life, be- 

 come automatic, or reflex, from habit : the mind is seldom 

 directed to them, but delegates their control to the medulla 

 and spinal cord. Thus a person in walking, may traverse 

 several miles while absorbed in thought, or in argument 

 with a companion, and yet be conscious of scarcely one in 

 a thousand of the acts that have been necessary to carry 

 his body from one point to another. By this admirable 

 and .beautiful provision, the mind is released from the 

 charge of the ordinary mechanical acts of life, and may 

 devote itself to the exercise of its nobler faculties. And it 

 is worthy of notice, that the greater the use of these facul- 

 ties, the more work does the reflex function assume and 

 perform ; and thus the employment of the one insures the 

 improvement of the other. 



60. Muscles called into play by certain reflex movements ? The somnambulist * 



61. What is said of walking and other acts in connection with the office per 

 formed by the medulla and spinal cord ? 



