250 Physiology. 



tice, it will be found, that the fingers of the other hand, 

 without special training, are also improved. 



Test by Compass Points. The delicacy of localizing 

 touch is usually tested in this way. The blunted points of 

 a light pair of compasses are allowed to rest gently on the 

 skin of various parts of the body. If the two points are 

 very close together, they will be/<?# as one pressure. That 

 part which can best distinguish, as two points of touch, 

 these blunt points, is considered the most sensitive. By 

 this test the tip of the tongue is the most sensitive, being 

 able to distinguish, as two separate points of contact, the 

 tips of the compasses when only one twenty-fifth part of 

 an inch apart. Following is the order of degrees of sensi- 

 tiveness : tip of tongue, tips of fingers, lip, tip of nose, eye- 

 lid, cheek, forehead, knee, neck ; while the middle of the 

 back seems least sensitive. 



Reference of Sensation to the Region of Nerve Endings. 

 If the " funny bone," or " crazy bone," be hit, i.e. if the 

 ulnar nerve be bruised against the bone, sharp pain may 

 be felt in the wrist and hand, and soreness of these parts 

 may be felt for days, though they are not in the least 

 injured, but only the nerve at the elbow. The currents 

 along this nerve rouse sensations that we have learned to 

 locate at the endings of the nerve fibers. If, then, owing 

 to injury, the currents start from the elbow, the brain still 

 refers them to the nerve endings in the hand and wrist. 

 So, too, after amputation of a hand or foot, there may 

 for years be sensations referred to the missing member, 

 probably due to irritation of the nerves of the stump. 



The Temperature Sense. Many cases are on record in 

 which, from accident or disease, the sense of touch was 

 lost and the temperature sense retained, or vice versa. 



