282 APPLIED PHYSIOLOGY 



4. Thirty-one pairs of nerves connect the cord with all 



parts of the body. 



5. The use of the cells is to send orders over the motor 



nerves when told to do so by the brain, and also 

 to send orders in response to information brought 

 to them by sensory nerves. 



6. Orders sent in response to sensations are reflex acts. 



7. Reflex acts are for protection, nutrition, and to relieve 



the brain from the drudgery of sending orders for 

 every detail of bodily movements. 



8. The reflex action in an educated spinal cord enables a 



person to work with skill. 



9. Restraint of excessive reflex acts constitutes self-control. 







DEMONSTRATIONS 



122. Procure a spinal cord at the butcher's. Notice the nerves 

 going off from the cord. Notice how the cord is enveloped by a thick, 

 fibrous sheath and is held in place by the nerves and fibrous bands. 

 Remove the cord from the bone and. slit open its sheath. Notice the 

 soft consistency of the cord and its shape like two cords pressed 

 together. On its clean-cut edge notice the grayish butterfly-shaped 

 center and the pure white outer part. 



123. Examine a thin cross section of the cord under the microscope 

 with at least 200 diameters. In the outer parts of the specimen notice 

 the round circles of cut nerve threads. Explain that this is the white 

 matter of the cord. 



Examine the central part, noticing the large nerve cells and nerve 

 fibers which run in all directions. Notice the fine and wavy connective 

 tissue fibers binding the whole together. 



124. The pure reflex action of the cord can be shown with a decapi- 

 tated frog. Place a small piece of blotting paper, wet with a strong 

 acid, upon its back, and it at once kicks it off with its hind leg. Prick 

 its back, and it makes one leap. Suspend it with its hind legs hanging 

 down, and let a toe touch a dish of acid, and it at once draws up the 

 leg. (See demonstration 35.) 



Explain that the frog has no feeling or sense, but performs the move- 



