? 5 6 A HA NUA L OF PH YSIOL COY 



long flight of stairs, and to answer the inquiries of the 

 surgeon. Finally, he recovered, and lived for nearly thirteen 

 years without either sensory or motor deficiency, except that 

 he suffered occasionally from epileptic convulsions. But his 

 intellect was impaired ; he became fitful and vacillating, 

 profane in his language and inefficient in his work, although 

 previously decent in conversation and a diligent and capable 

 workman. 



Localization of Function in the Central Nervous System. Let 

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

 localization of function. Scattered all over the grey matter of 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 dis- 

 tinct 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- 

 "Miotor centre in the bulb, for example, may in no essential respect 

 differ from that which goes on in the respiratory centre. The calibre 

 of the bloodvessels will alter in response to a change of activity in 

 the one because it is anatomically connected 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. 



Some recent experiments afford a very interesting illustration of the 

 determining influence of their peripheral connections on the function 

 of nerve-fibres. Langley divided (in cats) the vagus nerve and the 

 cervical sympathetic. The peripheral end of the former degenerated, 

 of course, below the section, and the peripheral (cephalic) end of 

 the latter degenerated above the section, up to the terminations of 

 its axons in the superior cervical ganglion. The central end of the 

 cut vagus was subsequently sutured to the peripheral end of the cut 

 sympathetic. After a time the vagus-fibres grew along the course of 

 the degenerated sympathetic up to the ganglion, where some of them 

 formed arborizations around the ganglion cells. It was now found 

 that stimulation of the vagus produced the effects usually caused by 

 stimulation of the cervical sympathetic; for example, dilatation of 

 the pupil and constriction of the bloodvessels of the head and neck. 

 From these experiments it follows that the functions of the various 

 groups of fibres in the cervical sympathetic do not depend on any- 

 thing peculiar to the fibres ; any fibre which can make connection 

 with one of the ganglion-cells that send axons to the dilator muscle 

 of the iris will, when stimulated, act as a pupillo-dilator fibre, just as 

 well as a cervical sympathetic fibre. 



