274 APPLIED PHYSIOLOGY 



SUMMARY 



1. The cells of the body are made to act harmoniously by 



means of orders sent from a few cells in a central 

 nervous system. 



2. A nerve is a bundle of microscopic threads, each run- 



ning from a central nerve cell to the cells of the 

 body. 



3. Nerves transmit impulses caused by irritation from out- 



side the body, and also impulses originated in either 

 the cells of the body or the central nerve cells. 



4. Sensory nerves carry from the cells news concerning 



a substance which is touching the body, and they 

 inform the central nerve cells when the cells are tired 

 or are in need of food. 



5. Motor nerves carry orders to the cells to move, to 



secrete, to eat, and to grow. 



6. Impulses in nerves travel about 100 feet per second. 



7. Nerves may become inflamed and produce pain and 



paralysis. 



8. Alcohol often produces severe inflammation of the 



nerves. 



DEMONSTRATIONS 



1 1 6. Skin the leg of a small animal or frog, and push apart the 

 muscles upon the inside of its upper part. White nerve cords will be 

 seen to lie alongside the main artery and vein, and can be traced up- 

 ward to the spinal cord and downward until they become lost in the 

 skin or muscles. Notice that those which branch off to the skin are as 

 large and numerous as those which supply all the rest of the leg. 

 Notice how much force is needed to break one of the nerves. In 

 ancient times it was supposed that tendons and nerves were the same. 

 Compare a nerve with a tendon to see their points of resemblance. 



117. To show the effect of irritating a nerve in its course, pinch a 

 boy's funny bone. He will wonder how the sensation travels to the 



