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Dr. H. Head. 



painful but also to all potentially unpleasant stimuli ; the itching, produced 

 by brushing the hairs of my hand, was more intolerable than any normal 

 sensation. Pleasurable stimuli also evoke an excessive response, and the 

 pleasure which accompanies moderate excitation of the heat-spots far exceeds 

 that obtained from general stimulation of the normal skin with the same 

 temperature. This exaggeration of the efifect produced by potentially 

 pleasurable stimuli forms a prominent feature in some cases of thalamic 

 over-action, and has not been dealt with adequately by any of our critics. 

 It cannot be explained by " irritation," nor is it a fortuitous perversion 

 of some normal function. On the other hand, it falls into line with all 

 the other phenomena we have attributed to loss of control. 



Integration is the main business of the central nervous system, and within 

 it the diverse effects produced on the living organism by external forces are 

 sorted, combined and inhibited. Should the functions, which have been 

 disturbed by an organic lesion, belong to the same level as those which are 

 unaffected, the loss of one group has no material effect on the other ; there 

 is none of that over-action so common, when dominant centres are destroyed. 

 When the lesion is situated in the lateral columns of the spinal cord, 

 sensibility to heat and to cold may be disturbed independently; but isolated 

 anaesthesia to heat over a certain part of the body is not accompanied by 

 over-reaction to cold or vice versd. At this point in their course through 

 the nervous system, the impulses underlying sensations of heat and cold 

 have already undergone qualitative integration ; they run side by side in 

 separate tracts and can be disturbed independently. Here they are equi- 

 pollent ; no one sensory activity is dominated by the other, and structural 

 changes produce loss of se;nsation unaccompanied by excessive responses. 



If, however, the factor eliminated by the lesion has exercised some control 

 over the functions which still remain intact, phenomena may appear which 

 were inhibited under normal conditions. Suppose half the scholars are absent 

 from a class, the sum total of its vital energy is diminished, but discipline is 

 maintained unimpaired ; absence of the master, on the other hand, leads 

 inevitably to disorder. 



But it would be wrong to suppose that removal of a dominant mechanism 

 reveals the reactions of a phylogenetically older organ in all their primitive 

 simplicity. The integrative activity of the higher centres has profoundly 

 modified the functions of those below them in the neural hierarchy; some 

 have been caught up to take part in the new complex, whilst others are held 

 in check or inhibited. Thus, the reactions obtained under favourable condi- 

 tions from the divided spinal cord in man are more specifically flexor than in 

 the dog or cat. For in the lower animals the specialisation of function is less 



