312 THE BODY AT WORK 



when it reaches the centres of consciousness, produces pain also 

 seems to call for an hypothesis of extra-neuronic conduction. 

 Any reference to pain in a work on physiology needs a few 

 words of preface, since popularly the term " pain " is used in 

 various senses. When I see pink geranium and nasturtiums 

 growing in the same flower-bed, I may exclaim : " It is positively 

 painful." The want of harmony, and at the same time the 

 insufficiency of contrast, of chalky pink and translucent orange, 

 jars my aesthetic sense. Dislikes, however well founded, are 

 ruled out in thinking of the physiology of pain. Further, in 

 defining pain, we must be careful to isolate the real thing, and 

 not to confuse it with sensations which seem to lead up to it. 

 If, putting my finger in a pair of pincers, I touch it as lightly 

 as possible, the first sensation is one of contact ; a little harder, 

 and it becomes a sense of pressure ; harder still, and all sense 

 of contact or pressure is lost in pain. It is usual to regard 

 pain as sensation carried to excess. But neither is this physio- 

 logical. An excessively bright light or an excessively loud 

 sound is disagreeable. It causes a sudden movement for the 

 purpose of avoiding it just such a movement as one would 

 make if one touched a red-hot poker but it is not, strictly 

 speaking, painful. Not uncommonly in cases of accident or 

 disease of the spinal cord a sharp distinction is drawn between 

 the sense of touch and the capacity for experiencing pain. 

 Below the injury the patient retains his sense of touch un- 

 diminished in acuteness, but no blow, or cut, or burn, causes 

 him any pain. The pain caused by squeezing the finger in a 

 pair of pincers is not, therefore, an excess of touch sensation. 

 Pain begins to be experienced in the skin just when the object 

 applied to it is affecting it to an extent which might do harm. 

 If the point of a needle touches it, it causes pain as soon as the 

 pressure is a trifle less than that needed to pierce its surface. A 

 hot object begins to hurt when the temperature reaches 48 C. 

 almost enough to coagulate the tissue fluids. Pain is not a 

 discriminative sensation. If I hold my arm out at right 

 angles, I am conscious for the first few minutes of its weight, 

 and have, besides, some sense of the traction exerted by the 

 muscle of the shoulder. At the end of ten minutes these 

 sensations are merged in pain, and for some time after lowering 

 the arm the shoulder-muscle aches, much as it does in rheu- 



