THE NERVOUS SYSTEM IN GENERAL. 745 



spinal cord hindered the manifestation of all movement in the muscles, when the 

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

 of the cord, on to the inferior roots, from the iiTitatiou due to this pinching ; 

 the property which permits the medullary axis to act in this manner is named 

 the rofiex power. It may be remarked that, if wc suppose for a moment the 

 superior and inferior ner\'e-roots to be united in an arch in the substance of 

 the spinal cord, this reflex property would be nothing more than the nervous con- 

 ductibility itself operating precisely in the direction special to each kind of nerves. 



This union really exists ; only the nerve-roots are not in communication, 

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

 sensitive is changed into motor excitabihty. 



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 local when they result from a slight irritation, 

 these movements may take place in all the muscles of the body after powerful 

 stimulation. 



Let us now inquire into the attributes of the encephalon. 



Excitability has been determined in several points of the medulla oblongata, 

 and in the interior of the cerebellum. Physiologists have long denied it to the 

 surface of the latter, and to the substance of the cerebral hemispheres ; but 

 within the last twenty years, Fritsch and Hitzig, Ferrier, Carville and Duret, and 

 others, have demonstrated that several points of the cerebral and cerebellar cortex 

 are excitable by electricity. The brain possesses conductibility, because 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 dis- 

 tinguishes the encephalon, is its action as a sensitivo-motor centre ; in it arrive 

 the stimuli from the sensitive nerves, and there they are felt and considered. 

 In the brain arise the motor excitations which result in spontaneous voluntary 

 movements. 



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

 lation, and in which death has been prevented by artificial respiration, observation 

 demonstrates that sensibility and spontaneous motricity are preserved in the 

 head, the nerves of which are in direct communication with the brain. Pinch 

 the upper lip, and the creature testifies by the movements of this part 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 hungTy, and endeavours to satisfy this craving by seizing the 

 food within its reach, and masticating and swallowing it. After this demon- 

 stration, it is no longer possible to doubt that, if an animal feels, it is by the 

 brain, and if it tvills, it is also by the brain. 



But sensihility and volition do not constitute the only attributes of the brain ; 

 for it is the seat of other manifestations not less interesting — those of the instincts 

 and intelliijencf. 



The brain also contains several special motor and sensory centres, the exist- 

 ence of which modern physiology and pathology have completely established. 

 These centres are situated in or on the surface of different parts of the organ. 



