176 THE HUMAN BODY 



Pain spots are more numerous than any of the others; touch spots 

 rank next in number, it being estimated that on the trunk and 

 limbs there are a half million of them; cold spots are only half as 

 numerous as touch spots; warmth spots are fewest of all, their 

 number being estimated at thirty thousand for the entire Body. 



Pain. When the skin is powerfully stimulated by heat, cold or 

 pressure, or is inflamed, we get a sensation which we call pain. 

 This is something quite different from the unpleasantness caused 

 by a dazzling light or a musical discord or a disagreeable odor or 

 taste. We recognize these as being still sight or sound or smell 

 or taste sensations. Pain, however, is always recognized as a 

 distinct sensation having its own modality. Its function seems 

 to be wholly one of warning; only when something is amiss 'do 

 we feel it. Since danger results from strong stimulation but not 

 from feeble stimulation pain receptors are less irritable than other 

 sorts ; it is estimated that the sense of touch is one thousand times 

 as delicate as the sense of pain. Harm may result from excessive 

 stimulation of any sort. Pain receptors, therefore, are irritable 

 to all forms of energy except that of light. 



Because pain results from any sort of stimulation, but only 

 when excessive, it was formerly thought to be not a distinct sense 

 but the result of overstimulation of the other senses. On this 

 theory it would be hard to account for the fact that skin pain is 

 so very different in modality from a touch or temperature feeling, 

 and to understand why it gives rise in consciousness to concep- 

 tions concerning a condition of the Body and not of some external 

 object: it is not extrinsically referred by the mind to a quality of 

 anything but the painful part itself, as a dazzling light sensation 

 or a fetid odor is. There is also experimental and pathological 

 evidence that the paths taken in the spinal cord by nerve impulses 

 causing pain are different from those leading to a consciousness 

 of touch. If certain parts of the cord are cut in the thoracic 

 region of a rabbit, gentle touches on the hind limb appear to be 

 felt; the animal erects its ears or moves its head: but powerful 

 stimulation of the sciatic nerve causes no signs of pain, while if 

 the dorsal white columns be cut the animal still can feel stimuli 

 applied to the hind limb and sufficient to cause pain under normal 

 conditions, but it appears insensible to gentle pressure on the 

 skin. In human beings very similar phenomena have been ob- 



