202 



Dr. H. Head. 



to stimuli, which produce alterations ia form or pressure.* Excessive 

 tension may evoke pain, and " cramp " is the response of these end-organs 

 to abnormal muscular contractions. Parts innervated in this manner are 

 insensitive to light contacts, pricking, heat and cold; but they are so 

 endowed with definite local signature, and the patient is capable of 

 appreciating within certain limits the site of the stimulated spot. It is 

 this system which is responsible, not only for the muscular pains of 

 intestinal colic, but also for the local pain and tenderness on pressure, 

 associated with inflammation of the serous membranes, such as the peri- 

 cardium, pleura and peritoneum. In fact, these cavities behave like the 

 inner surface of joints ([4], p. 93 and [6], pp. 157 and 232). 



But the internal organs are also supplied from another neural system, 

 equivalent, we believe, to the cutaneous punctate mechanism. Even in the 

 skin, the pain-spots are far more numerous than those for heat and cold ; 

 protopathic sensibility is essentially a warning mechanism, and most 

 of the viscera, excepting the oesophagus and bladder, seem to be devoid of 

 all sensory response to purely thermal stimulation, as might have been 

 expected from their sheltered position. 



One of the most striking characters of pain, or indeed of any sensation, 

 evoked from my hand in a protopathic condition, was its tendency to be 

 referred into remote parts. Portions of the skin seemed to be linked up 

 together in a peculiar manner, so that a stimulus applied to the one pro- 

 duced a diffuse outburst localised in the other. When pain of this order 

 has been aroused in the visceral system, the sensation may be referred to 

 the surface of the body, which becomes tender to cutaneous stimulation. 

 This is not a " hyperalgesia," but a tendency to react more vividly to any 

 excitation capable of evoking discomfort. The threshold to pricking is 

 not lowered, but the vehemence of the response, both sensory and reflex, 

 is greatly increased. 



Now this over-reaction is associated with reflexes which still reveal their 

 old impulsive character. The abdominal muscles become tonically con- 

 tracted, and the leg is drawn up on the affected side. The sufferer is forced 



* Afferent impulses, due to changes in the volume of the lungs, belong to this deep or 

 proprioceptive group [3]. They give rise to the Hering-Breuer reflex ; inflation produces 

 an expiratory effect, whilst diminution in volume acts as an inspiratory stimulus. I was 

 able to show that this did not depend on the absolute, but on the relative size of the 

 lung ; thus the same volume might produce either an inspiratory or an expiratory effect, 

 according to whether it was reached by allowing the lung to collapse or by increasing 

 its content. Moreover, such stimuli evoke a strong negative after-action in the respira- 

 tory centre, so that long continuance of one form of stimulation favours response to its 

 opponent ; they exhibit, in fact, a remarkable example of biphasic activity. 



