2/0 APPLIED PHYSIOLOGY 



is a slight sensation caused by contact of the skin with an 

 object. By means of it such ideas as those of shape, 

 smoothness, size, and dampness are gained. 



Different parts of the body vary greatly in the ability of their nerves 

 to detect slight differences between two sensations. Thus the ends of 

 the fingers distinctly feel two points T \ inch apart as separate points, 

 while if two points are applied to the back, they seem as one point 

 until they are separated two inches. So we naturally use the ends 

 of the fingers to feel with. 



486. Sensations of temperature. In the skin special 

 nerves seem to end in minute points which are situated 

 from ^g to J- of an inch apart. When these are touched, a 

 sensation of heat or cold is felt, while the skin between 

 feels only a touch or pain. Some spots give a sensation 

 of cold only, and others of heat only. 



Sensations of extreme heat or of extreme cold cease to be feelings of 

 temperature, but are felt only as pain. The skin is so sensitive that it can 

 detect a difference of of a degree of temperature between two objects. 



487. Painful sensations. A sensation of touch or of 

 temperature, if greatly increased or often repeated, be- 

 comes unpleasant and is called a pain. The same sensa- 

 tion may be felt at one time as a pleasant touch and at 

 another as a pain. When an influence is becoming great 

 enough to endanger the body, it arouses the nerves of 

 pain and produces a strong and unpleasant feeling which 

 overpowers the simple sensation of touch and compels us 

 to withdraw from the danger. Pain is a protection for the 

 body and not altogether an evil or a punishment. When 

 the nerves of pain in an arm or leg are diseased, the 

 limb may be burned beyond recovery without a person's 

 knowledge. In many diseases pain is a prominent symp- 

 tom, and the physician is besought to give it relief. Yet he 



