Release of Function in the Nervous System. 



201 



Thus, afferent impulses from the viscera do not normally enter conscious- 

 ness. The eupeptic knows nothing of the processes of digestion beyond a 

 certain gentle sense of well-being. But under abnormal conditions afferent 

 impressions from the internal organs are capable of arousing pain and 

 discomfort. These parts are probably innervated, like the glans penis, from 

 the deep and protopathic systems ; but unlike the glans their sensibility is 

 extremely low. All power of conscious response to heat and cold is certainly 

 absent from the greater part of the stomach and intestines, and pain cannot 

 be produced by burning, cutting, and the prick of a pin or other sharp 

 instrument. Internal surfaces are unable to respond to artificial stimuli 

 to which they have never been exposed during the life of the individual 

 or the race. But the hollow viscera, such as the stomach and bladder, 

 react briskly to changes in tension which are their natural mode of 

 stimulation. 



Even if a stimulus is capable of exciting these sheltered parts of defective 

 sensibility, it does not usually produce a sensation on account of the resist- 

 ance of the nervous system to such potentially painful impressions. But 

 a sensory response may be evoked whenever these visceral impulses become 

 sufficiently strong to overcome the inhibition, or the forces opposing their 

 passage are in any way. diminished. Once the path has been opened and 

 the dominance of the higher reflexes overcome, a weaker visceral stimulus 

 will be followed by sensation ; to this diminished resistance is due the 

 production of pain from otherwise inadequate causes, where visceral irritation 

 has been long continued. 



Thus, under favourable conditions, afferent impulses from the viscera are 

 capable of arousing pain and discomfort. But this does not of necessity 

 point to the part diseased ; the pain may be a manifestation of abnormal 

 activity on the part of healthy organs, to which they have been excited 

 by a morbid process elsewhere. In the earlier stages of inflammation of 

 the appendix or with affections of the gall-bladder, the pain may be due 

 to abnormal movements of the stomach and intestine ; under such conditions 

 it expresses the response of normal parts to a lesion situated in some allied 

 physiological system. 



Now we have reason to believe that the viscera have a double afferent 

 supply ([9], p. 64). One of these corresponds to that deep system, which in 

 the limbs supplies muscles, tendons and joints, and remains intact, when all 

 cutaneous nerves are severed ([9], p. 246). This gives rise to Sherrington's 

 proprioceptive reflexes, that have so profound an influence on the regulation 

 of posture and movement. The peculiar aptitude possessed by a part 

 innervated from this deep afferent mechanism, is the power of responding 



