162 THE NERVOUS SYSTEM. 



terprets all injuries of the trunk of a nerve. Sensation or 

 pain is not felt at the point of injury, but is referred to the 

 outer extremities of the nerve, where impressions are habit- 

 ually received. This is the reason why, after a limb has 

 been amputated by the surgeon, the patient appears to 

 suffer pain in the member that has been severed from the 

 body ; while some form of irritation at the end of the nerve 

 in the wound, or stump, is the real source of his distress. 

 Again, when the "funny-bone" that is, the ulnar nerve 

 at the elbow, is accidentally struck, the tingling sensa- 

 tions thus produced are referred to the outer side of the 

 hand and the little finger, the parts to which that nerve is 

 distributed. 



27. All the spinal nerves, and two from the brain, are 

 concerned in both sensation and motion. Of the remainder 

 of the cranial nerves, some are exclusively motor, others 

 exclusively sensory; and still others convey, not ordinary 

 sensations, but special impressions, such as sight, hearing, 

 and smell, which we have yet to consider. However much 

 the functions of the nerves seem to vary, there is but little 

 difference discoverable in the nerves themselves, when ex- 

 amined under the microscope. Whatever difference exists 

 must be. accounted for in consequence of the nerves com- 

 municating with different portions of the gray matter of 

 the brain. The rate of motion of a message, to or from 

 the brain along a nerve, has been measured by experi- 

 ment upon the lower animals, and estimated in the case of 

 man at about two hundred feet per second. As compared 

 with that of electricity, this is a very slow rate, but, in 

 respect to the size of the human body, it is practically in- 

 stantaneous. 



28. The Functions of the Spinal Cord. As the 



27. The ppinal nerves, and two from the brain ? Of the remainder? Difference 

 in the nerves ? How accounted for ? The rate of conduction along a nerve ? As 

 compared with electricity? 



28. Function!* of the anterior and posterior column? of the cord ? If the cord 

 be divided ? 



