3OO ELEMENTS OF PHYSIOLOGY 



as a blessing. Some people interpret the blessing as an 

 opportunity to do what? 



5. Name six articles which God has warned us are in- 

 jurious by giving them bitter, burning, or nauseating tastes, 

 yet which are used by man. 



6. Name six feelings which are intended as warnings 

 for our guidance, but which are commonly disregarded. 



THE BRAIN 



556. The spinal cord can act only in response to im- 

 pulses at the moment they are received. The brain can 

 originate impulses which are not in direct response to a 

 stimulus from the outer world. Its acts are apparently 

 spontaneous, but they probably result from the combina- 

 tion of impulses previously received, which memory has en- 

 abled it to store up and retain. The brain not only causes 

 action and directs the cord in giving order to voluntary 

 movements, but it can restrain excessive action in the spinal 

 cord. Self-control comes largely through the power pos- 

 sessed by the brain of restraining the spinal cells from 

 sending out reflex impulses when strong and sudden im- 

 pulses are received from the outer world. This is called 

 the inhibitory power. If a door slams, a person whose 

 brain is not exerting good control jumps suddenly. 



557. The Coverings of the Brain. What facts did you 

 learn about the skull, showing that it is well constructed 

 for protecting the brain ? The brain is covered by three 

 membranes ; the outer tough one lines the skull and the 

 spinal canal. The next is thinner. There is a lymphlike 

 fluid, called the cerebro-spinal fluid, within this membrane, 

 so that the brain is surrounded by a kind of water bed. 

 The third, and innermost covering, is hardly a membrane, 

 for it is merely a thin network of fine blood vessels and 

 connective tissue. It dips down into every depression and 



