THE NERVOUS SYSTEM 29 1 



diseases it is a prominent symptom, and the physician is 

 begged to give relief. But the wise physician hesitates be- 

 fore giving morphine or other sedatives, knowing that to 

 drown the pain is to conceal the danger, and take away his 

 best evidence as to the state of the disease. At the same 

 time, he runs a risk of starting a habit in the patient of 

 deadening pain and hiding unpleasant feelings by taking nar- 

 cotics, a habit that may become fastened upon the patient 

 and ruin his life. Hence when sick we should bear pain 

 bravely. 



533. Tickling is intermediate between touch and pain. 

 It is produced in parts which are supplied with few nerves 

 of touch, as under the arm. It may produce great suffer- 

 ing. Some persons who can endure great pain cannot 

 control themselves when tickled, as the movements excited 

 are largely reflex. Itching is a sensation akin to tickling. 

 It may be overcome by producing a greater sensation, as 

 by scratching. Sometimes it may be so great as to lead 

 a person to injure the skin seriously by deep scratching. 



534. The Muscular Sense. When an object is lifted, it 

 is felt to be distinctly heavier if its weight is increased by 

 only T a y> but when it is laid upon the skin, its weight must 

 be increased by \ before it feels heavier. Hence it is 

 concluded that sensations of weight and resistance to the 

 muscles depend upon the amount of muscular effort needed 

 to overcome the resistance as well as upon the feelings 

 of pressure upon the skin and body. 



535. If Motor or Efferent Nerves going to a muscle are 

 cut, there is paralysis of the muscle, so that there can be no 

 voluntary or reflex action in the part. If an efferent nerve 

 going to a gland is cut, the function of the gland will be almost 

 suspended. Even if food is taken into the mouth and the 

 sensory nerves carry the news to the brain, the efferent 

 nerve being cut, no impulse can return and the secretion 

 will be very slight. When the motor nerve to a part is 



