THE NERVOUS SYSTEM IN GENERAL. 657 



I will suppose that an animal has had its spinal cord cut across in the 

 lumbar region, and I excite, by pinching, one of the superior roots re- 

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

 to the brain, as this part is isolated from it ; and yet movements take place 

 in the muscles of the posterior members. Does it happen that, after section 

 of the medulla, the conductive property of the nervous fibres which originate 

 superiorly is interverted and changed into centrifugal conductibility ? No; 

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

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

 excitation 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 

 cord hindered 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 named 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 conductibility 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, 

 mt 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 

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

 X)dy after an energetic stimulation. 



Let us now inquire into the attributes of the encephalon. 



Excitability 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 

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

 nor yet in the cerebral hemispheres. The brain possesses conductibility, 

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

 departure for, all the excitations. In fine, the encephalic mass should 

 possess neurility like the nerves, but this general property is more or less 

 modified. What more particularly distinguishes the encephalon is its action 

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

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

 excitations which result in spontaneous voluntary movements. 



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

 articulation, and in which death has been prevented by artificial respiration, 

 observation demonstrates that sensibility and spontaneous motricity are 

 preserved in the head, whose nerves are in direct communication with the 

 encephalon. Pinch the upper lip, and the patient testifies by the movements 

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

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

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

 the eye from their contact. More striking still, the animal feels hungry, 

 and endeavours to satisfy this craving by seizing the food within its reach, and 



