I 



KERVOTJS SYSTEM. 125 



change fasciculi. By this means each nerve passing off from the plexus 

 has a wider connection with the spinal cord and more extensive sym- 

 pathies. ^ Again it is by this means that groups of muscles are associated 

 for combined action. 



Nez*ve-centres have the power of originating the sensitive impulses, by 

 which muscles are excited to action and various functions are performed ; 

 but few or no motor impulses proceed spontaneously from nen^e-centres. 

 Nerve-centres have also the power of transferring the impressions, which 

 reach them through the centripetal nerve fibres, and thereby of diffusing 

 impressions. Nerve force is by some considered to be allied to electricity! 



243. Functions of the Nervous system. 



The functions of the Nei-vous System are : 1st, Sensation ; 2nd. Voluu- 

 taiy motion; 3rd, Co-ordination of motion; 4th, Reflex action; 5th, the 

 motions connected with the processes of nutrition, secretion, &c. 



Stimuli^ applied to nerves first increase and then depress their excita- 

 bility. Narcotics have the power of deadening or of entirely destroying 

 the excitability of the nerves. The action of the nerves is also affected 

 by temperatui-e. 



244. Influence of the Nervous system u:ith reference to disease. 



So far as regards the physiologA' of the neiwous system. Bevond this 

 the medical enquirer is almost lost. Yeiy little is really known of the 

 agencies at work in this system. Nervous influence is the most impor- 

 tant and yet the most mysterious influence in life. The nerves them- 

 selves we can trace. We know that they are given off from or, as others 

 think, run to the brain and spinal cord from all parts of the bodv. We 

 know that sensation felt at one extremity of the body is transmitted with 

 more than electrical rapidity to the brain, and thence re-transmitted to 

 the point at which the sensation is felt. The point of the nerve affected 

 has no sensibility except as connected with the brain. Nerves are merely 

 conductors of nervous impressions. They have no power of themselves 

 of generating force. They require a stimulus in order to manifest their 

 functions. 



Disease of any part is, Ave know, connected in some way with disturb- 

 ance of the nervous system of the part. Yet we cannot, we do not know 

 how to treat the real malady ; we treat the effect as we best can. Take, 

 for instance, a simple case of accelerated pulse. The acceleration is 

 doubtless due to nervous disturbance. Yet we cannot treat directly the 

 real cause. We may give cooling drinks, reduced diet, kc, and so we 

 succeed in lowering the tone of the system. Indirectly and in time our 

 remedies, no doubt, affect the nervous system; but directly we are not 

 able, in the present state of knowledge, to touch the real cause. Besides 

 Avhich there is at all times great difficulty in ascertaining the causes 

 which tend to produce a lowered or excited state of the nervous system. 



