THX NERVOUS 8Y8TXM i\ >. i:\iKAL. G57 



I will suppose tlint an aiiiinul lias had its spinal cord cut across in the 

 lumliiir region, an. I 1 excite, by pinching, one of the 8U]>erior roots re- 

 maining intact on the caudal portion. The stimulus cannot be conducted 

 to the bruin, us this part is isolated from it ; :ind yet movements take place 

 in tlie niusclt s of the posterior members. J >ocs it happen that, after section 

 of the medulla, the conductive property of the nervous fibres \vhichoriginate 

 superiorly is intervened and changed into centrifugal eonduetibility ? No: 

 for after the transverse section of these roots, the irritation of their central 

 end products exactly the same effects. It must be, therefore, that the 

 .'.tion had first reached the medulla, and was then transmitted by it to 

 the muscles by means of the centrifugal current fibres. And this is really 

 what occurred ; the section of the whole of these fibres on the trunk of the 

 eord hindcn d the manifestation of all movement in the muscles when the 

 superior roots were touched. There is, as has been said, reflexion in the 

 substance of the cord, on to the inferior roots, from the irritation due to this 

 pinching, and the property which permits the medullary axis to act in this 

 manner is nunud. the reflex power. It may be remarked that, if we suppose 

 for a moment the superior and inferior nervous roots to be united in an 

 arch in the substance of the spinal cord, this reflex property would be 

 nothing more than the nervous couductibility itself operating precisely in the 

 direction special to each kind of nerves. 



This union really takes place ; only the nerve-roots are not in communi- 

 cation, except through the medium of the cells in the grey substance, in 

 which the sensitive is changed into motor excitation. 



The reflex power is extinct immediately after death occurs in Mammals, 

 but it may last for several hours, or even for a day, in a decapitated animal 

 in which asphyxia has been averted by pulmonary insufflation. The extent 

 of the movements it determines is in relation to the intensity of the stimulus 

 which is the primary cause of it; merely localised when they result from 

 a slight irritation, these movements may take place in all the muscles of the 

 body after an energetic stimulation. 



- now inquire into the attributes of the encephalon. 



Ability is not remarked in all parts of the brain; it exists in 



several points of the medulla oblongata, and in the deep substance of the 



.Hum ; but it cannot be rendered evident on the surface of the latter, 



in. r yet in the cerebral hemispheres. The brain possesses eonduetibility, 



because the grey substance composing it is the receiver of, and the point of 



d'-j.arture for, all the excitations. In fine, the encephalic mass should 



sg neurility like the nerves, but tliis general property is more or lees 



modified. What more particularly distinguishes the encephalon is its action 



as a tetuitioo-motor centre; in it arrive the excitations from the sensitive 



nerves, and there they are felt and judged. In the brain arise the motor 



tatious which result in #pontaneou* voluntary movement*. 



In an animal paralysed by division of the cord at the occipito-atloid 



Dilation, ami in which death bus been prevented by artificial respiration, 



rvation demonstrates that sensibility and spontaneous motricity are 



in the head, whoso n< : n direct communication \\ith the 



I'haloii. Pinch the upper lip, and the patient t. stifles by the movements 



of this organ that it feels pain. Pass the linger towards the eye. and the 



:s are twinkled and closed: a proof that the animal sees objects, 



uppnciatis the distance which separates it from them, and tries to remove 



the eye from their contact. More striking still, the uninuil feels bin 



ivours to s:i!isl v this craving by seizing the food within its iv.ich, and 



'2 U 



