296 ADVANCED PHYSIOLOGY 



of the left half with the right side of the body. Doubtless the 

 student has known of a case where some part of a person's 

 body is paralyzed. As a rule, whichever side of the body 

 is affected, the trouble is on the opposite side of the 

 brain. As a proof of this, if the brain of an animal is laid 

 bare and then stimulated in spots with electricity, the move- 

 ments which result are always on the side of the body oppo- 

 site to that on which the brain is stimulated. Paralysis 

 sometimes results when a blood vessel has broken and a clot 

 causes pressure on some part of the cortex; if the clot can be 

 removed, the patient may entirely recover. Other causes 

 of paralysis will be noted in connection with the spinal 

 nerves. 



The fibres in the center of the cerebrum are concerned 

 wholly with carrying nerve messages or impulses, never in 

 originating or receiving them. Figure 150 shows the courses 

 of some of these fibres of white matter. In the performance 

 of one's varied motions, it is evident that the most intimate 

 connection between the two sides of the brain must be es- 

 tablished. The right and left sides of the body, and both 

 arms and legs are doing things which must be directed toward 

 the same end in an orderly manner. The figure shows that 

 some fibres put the two halves of the cerebrum into com- 

 plete communication with one another. The different cells 

 of the same side are also connected since they govern such 

 different muscles and must be completely harmonized in their 

 actions. No picture can represent accurately all of these 

 fibres, nor would it be possible to follow them all, so numerous 

 are they. It is necessary merely to keep in mind that these 

 cells are all in ready communication with one another, and 

 thus work together in the control of the thousands of muscle 

 movements in the body. 



Cerebral Localization. The use of these fibres becomes 

 very easy to understand when we note that certain parts of 

 the brain have special work to do. The functions of the cells 



