142 HUMAN PHYSIOLOGY 



They have to do with those sensations which are called 

 kinesthetic, those feelings which we have respecting 

 our posture, and our ability to realize our own move- 

 ments. One need not look at the extremities to see 

 how they are disposed; there is sensory evidence of 

 one's position at all times. 



Our temperature sensations, also, lie in a class inter- 

 mediate between the varieties which are clearly special 

 and those which are necessarily general. If a small 

 object touches the skin we say that the object is hot or 

 cold ; we do not consider that the patch of skin has taken 

 the temperature of the thing in contact with it. But 

 if the whole surface of the body is warmer than usual 

 we may say either that the room is warm or that we 

 are. 



Under the head of special sensations we have those 

 produced by the stimulation of the skin and those 

 pertaining to taste, smell, hearing, and vision. In 

 other words, these are the five senses with the qualifica- 

 tion that what is called touch is multiple. It is to be 

 resolved into pressure, warmth, cold, and probably 

 surface pain. Surprise may be expressed that warmth 

 and cold should be separately mentioned. But we 

 have pointed out elsewhere that the physical conception, 

 according to which cold is merely less heat, cannot be 

 applied to such a system as this. Cold stimulates nerve- 

 endings as truly as does warmth and with equally positive 

 results. 



If all nerve-impulses are alike how can we explain 

 the three or four distinct sensory capacities of the skin? 

 There is only one resort to assume that there are as 

 many separate sets of receptors as there are sensory 

 qualities. This is the usual belief. Close study of the 

 responses to be obtained from the skin has shown that 

 there are minute areas which are capable of furnishing 

 one sensation and no more. Thus there are pressure 

 points, warm points, cold points, and pain points, ac- 

 cording to the standard description. An area with one 



