THE NERVOUS SYSTEM 



303 



times the power of motion is lost below the injured point. 



If the power of motion is lost, e.g. the motion of the leg, then 



the injury must be in a descending tract, where the messages 



that pass from the brain down to the leg have been interfered 



with. If the person <: 



loses the sensation of cP* 



feeling so that he has no 



consciousness of anything 



that may touch a given 



part of the body below 



the injured spot, then it 



is assumed that an 



ascending tract has been 



severed. 



By these studies the 

 areas which are devoted 

 to impulses going in one 

 direction or the other 

 have been determined 

 approximately as in 

 Figure 155. Roughly 

 speaking, all ascending 

 impulses go up to the 

 brain either on the poste- 

 rior side or on the right' 



FIG. 156. DIAGRAM 



Showing the course of the ingoing and outgoing 

 impulses in the cord. 



and left lateral regions 



near the surface; while 



the descending impulses 



pass downward on the anterior side or in the deeper layers 



of the lateral regions. 



One unexpected fact, however, comes to light in studying 

 the nerve paths in the spinal cord. An injury on one side 

 of the cord is, as a rule, accompanied by loss of sensation on 

 the other side of the body but not on the same side as the 

 injury. The conclusion is that messages brought into the 



