246 EXPERIMENTAL GENERAL SCIENCE 



nerve endings and a sensation is carried to the brain which 

 results in some kind of motor impulse being sent to the muscles 

 or other organs. 



208. The Brain. The upper and forward part of the brain 

 is known as the cerebrum. It is here that impulses involving 

 intelligence, memory, the emotions, and the will originate. 

 The cerebrum is divided by a deep groove into a right and 

 left hemisphere and consists of white and gray matter, with the 

 gray matter, which is made up of nerve cells, on the outside. 

 Below and back of the cerebrum is the cerebellum or little brain, 

 whose chief function is to coordinate the action of the muscles 

 and cause them to cooperate properly in carrying out the 

 directions of the cerebrum. Below the cerebellum, where 

 the spinal cord connects with the brain, is an enlarged portion, 

 the bulb or medulla oblongata. This part, in addition to other 

 functions, controls the beating of the heart, breathing, diges- 

 tion, secretion, and other processes not directly under control 

 of the will. 



209. The Spinal Cord. The spinal cord extends down along 

 he spinal column and, like the other parts of the brain, con- 

 sists of gray and white matter, though in this instance their 

 positions are reversed, the white matter being on the outside. 

 The white matter is the part over which nervous impulses 

 travel to and from the brain, while the gray matter consists of 

 nerve cells which enable the cord to act like the brain on 

 occasion. 



210. Involuntary Action. The human body is largely auto- 

 matic and carries on many of its processes without conscious 

 effort, in fact, over most of the functions upon which depend 

 the health and well being of the body, the mind has no control 

 whatever. In some cases, such as breathing and winking, we 

 may exercise voluntary control for a short time, but ultimately 

 the involuntary centers take up the work. By taking thought, 

 we may increase or diminish the length of a breath, but it 



