94 THE CENTRAL NERVOUS SYSTEM 



When the afferent field is still more restricted, as in the head of a dog 

 grafted on the circulation of another dog by anastomosis of the blood- 

 vessels, with precautions to avoid interruption of the blood-flow, not 

 only does the respiratory centre continue to discharge itself with a 

 regular rhythm, but cortical volitional movements persist (Guthrie, 

 Pike, and Stewart), and, so far as can be judged, sense perception, 

 emotional, and even intellectual, processes continue. In one case the 

 picture presented by the engrafted head was essentially the same as that 

 presented by the head of the ' host ' for over two hours. In a trans- 

 planted head from a younger dog in which the circulation had been 

 interrupted for twenty-nine minutes, a remarkable return of cerebral 

 function was observed (Guthrie). 



Localization of Function in the Central Nervous System. Lei 

 us now consider a little more closely the real meaning of this 

 localization of function. Scattered all over the grey matter oi 

 the primitive neural axis, and, as we have seen, over the grey mantle 

 of the brain as well, are numerous ' centres ' which seem to be 

 related in a special way to special mechanisms, sensory, secretory, 

 or motor.* The question may fitly be asked whether those centres 

 are really distinct from each other in quality of structure or action, 

 or whether they owe their peculiar properties solely to differences 

 in situation and anatomical connection. It is clear at the outset 

 that the nature of the work in which a centre is engaged must be 

 largely determined by its connections. The kind of activity which 

 goes on in the vaso-motor centre in the bulb, for example, may 

 in no essential respect differ from that which goes on in the respira- 

 tory centre. The calibre of the bloodvessels will alter in response 

 to a change of activity in the one because it is anatomically con- 

 nected with the muscular coat of the bloodvessels. The rate or 

 depth of the respiratory movements will alter in response to a 

 change of activity in the other, because it is connected with muscles 

 which can act upon the chest -walls. 



Experiments on the anastomosis of nerves afford a very interesting 

 illustration of the determining influence of their peripheral con- 

 nections on the function of nerve-fibres. It has, in fact, been 

 shown that the central end of any efferent somatic fibre i.e., any 

 fibre running from the central nervous system and ending in 

 striated muscle can make functional connection with the periph- 

 eral end of any other efferent fibre of the same class, whatever be 

 the normal actions produced by the two fibres. Advantage has 

 been taken of this in surgery. For instance, in a case of severe 

 facial (motor) tic the facial nerve was divided, and its peripheral 

 end united with a portion of the fibres of the spinal accessory. The 

 voluntary movements of the face, after regeneration had occurred, 

 were normally carried out through impulses descending the spinal 

 accessory. In cases of local paralysis, due to destruction of anterior 

 horn-cells (anterior poliomyelitis), restoration of movement has 

 also been obtained by connecting the motor nerve of the paralyzed 



