308 



THE CAT. 



[CHAP. ix. 



centres, with which, the internal ends of the efferent and afferent 

 fibres internal end organs are connected. 



This opinion has been reinforced by the fact that after severe 

 injuries to the spinal cord, parts supplied with nerves which take 

 origin below such injury, become deprived both of sensibility and of 

 the power of voluntary motion, while irritation of the cut surface of 

 the proximal part of a divided nerve in a limb stump may produce 

 a sensation, which feels as if it took place in parts which 110 longer 

 exist as, e.g., in the toes, when the leg has been amputated. But 

 in fact these phenomena are susceptible of another explanation, and 

 one which admits the belief that sensation occurs there where it 

 appears to occur and not far away in the central part of the 

 nervous system. For as the completion of the electrical or magnetic 

 circuit is necessary for electric or magnetic discharge, so a certain 

 integrity of the nervous structure is necessary for the result of 

 nervous action in motion or sensation, even though such sensation 

 really take place at that part of the body where it seems to be felt. 

 When, however, the integrity of the nervous structures is impaired, 

 the motor or sensitive nervous activity is correspondingly impaired, 

 and the occurrence of non-natural and abnormal sensations might 

 be a priori expected to arise under such non-natural and ab- 

 normal structural conditions. The occurrence of abnormal and 

 more or less delusive feelings after structural injury, by no means 

 proves that sensation is not peripheral under normal conditions. It 

 only proves that while nervous integrity is a sine qua non of normal 

 sensation, it is not a condition for the occurrence of all sensation, 

 but admits of the occurrence of feelings of an abnormal and 

 accidentally delusive character. 



It has also been very often assumed and supposed that the dis- 

 tinctions between the functions of nerves (i.e., whether they are 

 sensitive or motor) is due to some special endowment of the nerves 

 themselves, and not merely to the connexions which they may 

 happen to have. Now, however, it seems more probable that most, 

 if not all, nerves are essentially similar as regards their own intrinsic 

 powers, but that different nerves have practically different functions, 

 because their connexions are different. According to this view, any 

 nerve going from a nervous centre to a gland must have for its 

 function the promotion of secretion ; any nerve going from a centre 

 to a muscle must have for its function the production of motion, 

 and any nerve going from a peripheral end organ to a centre must 

 have for its function either the promotion of sensation or reflex 

 action. 



Whether this view be or be not correct, nerves, as we actually 

 find them, are either centripetal or centrifugal in their action, and, 

 as a rule, nervous influence can only be propagated in one direction 

 in any particular nerve. It may be that some nerves are inhibiting 

 ones, i.e., they are nerves which proceed from centres to the vicinity 

 of other [nerves, and, by their influence, check or neutralize the 

 actions of the latter, 



