Release of Function in the Nervous System. 207 



lesion can be attributed to this cause. On the other hand, protopathic sensi- 

 bility is extremely common and occurs solely over parts where finer sensory 

 discrimination is defective. Trotter [19] has put forward the theory that 

 these peculiarities of response are due to exposure of the constituent elements 

 of the closed nervous system to the irritative effect of contact with somatic 

 tissues. Even this view will not explain the abnormally vivid pleasure which 

 may constitute one of the factors in protopathic over-response. It does not 

 help us to understand the peculiar form assumed by the sensibility of the 

 normal glans penis. Nor can it account for the transitory regression and 

 recovery in the sensory condition of my hand during the second stage of 

 recovery after exposure to the injurious effects of cold. The vividness of 

 response and reference into remote parts returned ; but they disappeared 

 again when the sensibility of the hand was restored by warmth. 



No one has attempted to apply this conception of the irritative effect of 

 contact with somatic tissues to the phenomena of thalamic over-reaction or to 

 other analogous conditions. On the other hand, we have tried to explain 

 such manifestations of over-activity, whether motor or sensory, due to a purely 

 destructive lesion of the nervous system, by the general law of release of 

 subordinate functions. 



(3) The conception of levels of activity within the nervous system was one 

 of the fundamental aspects of Hughlings Jackson's teaching. To him a 

 " level " was always one of function rather than of structure. So, whenever 

 I have spoken of higher and lower centres, these must be considered as 

 nodal points of neural activity, and not of necessity as anatomical structiires. 

 In the illustrations, chosen to support my thesis, they were anatomically 

 separable ; for otherwise it would have been impossible to prove my con- 

 tention, that removal of a dominant activity, was responsible for the 

 phenomena under investigation. 



(4) Eemoval of a dominant neural mechanism permits the activity of lower 

 centres to appear. These unfettered manifestations are not fortuitous patho- 

 logical states, but represent that part of a complex reaction, which still 

 remains active ; they display characters more primitive than those of the 

 complete functions in which they normally play a part. The response is 

 massive and of unusual extent and vigour ; on the motor side it may affect 

 organs which do not normally lie within its reflex arc. Such stereotyped 

 reactions can be excited indifferently from an unusually wide field. They are 

 impulsive and assume the form of a warning or defensive response, regulated 

 more definitely by the extent than by the degree of intensity of the stimulus. 



But release from control due to a destructive lesion does not reveal such 

 lower activities in all their original simplicity ; for in most cases they have 



