310 



THE CAT. 



[CHAP. ix. 



If the spinal cord be cut through, it is impossible for the injured 

 animal either to feel any irritation which may be applied to parts 

 the nerves of which take origin below the division, or by any 

 voluntary effort to move any such parts. Nevertheless movements 

 of such parts may be produced by stimuli applied to them, without 

 the occurrence of either conscious sensation or voluntary effort. 

 Such unconscious movement in response to unrecognized stimuli is 

 called REFLEX ACTION. This shows that the cord itself must be a 

 centre capable of initiating responsive action of turning, as it were, 

 unfelt sensitive impulse into involuntary motor impulse. It does, 

 in fact, that which the brain does ; but does it, at least when thus 

 mutilated, without the accompaniment of any perceived sensation. 

 This kind of action is also called automatic or excito-motor, and it is a 

 curious fact that responsive movements of this kind are more 

 energetic than they would normally be, owing possibly to the spinal 

 centres being entirely devoted to the reflex action, and not at all by 

 the transmission of influence to the brain. 



But reflex action may take place in the uninjured condition, as during 

 sleep or under the influence of chloroform. Even when awake the 

 sudden and involuntary withdrawal of the foot from an irritating 

 object is an instance of essentially the same kind of action, though 

 since sensation here intervenes, such an action is spoken of as 

 Benson-motor, and is not exclusively due to the action of the spinal 

 cord. But, in fact, all action is " reflex " in the widest sense of that 

 term, i.e., including sensori-motor action. For all animal actions 

 which do not result from unfelt stimuli (internal or external) result 

 from felt stimuli. 



SENSATIONS are capable of RADIATION or TRANSFERENCE, as where 

 disease in the hip may produce pain in the knee-joint, or as, during 

 neuralgia, when pain proceeds from the part supplied by one branch 

 of a nerve to parts supplied by other of its branches. 



33. As to the FUNCTIONS of the MEDULLA OBLONGATA, it appears 

 to transmit and transfer influences in essentially the same way as 

 the spinal cord does as when irritation of the stomach produces 

 headache, or when pain in one tooth results in pain in the corre- 

 sponding tooth of the other side. The sensory impulses proceed 

 through the restiform bodies (which are extremely sensitive to touch) 

 and the motor ones, through the anterior pyramids. The division 

 of either pyramid results in motor paralysis, but, owing to the 

 decussation of their fibres, a paralysis of the side of the body opposite 

 to that of the division, supposing the cut to be made above the place 

 of decussation. Similarly, paralysis of the opposite side of the body 

 follows from destruction of one half of the encephalon above such 

 decussation. The function of the olivary bodies is unknown. 



The medulla is the seat of many reflex actions, such, e.g., as 

 sneezing, coughing, closing the eyelids, swallowing, and the respira- 

 tory actions. After the insensibility produced from concussion of 

 the brain or from chloroform, food placed far back in the mouth will 

 be swallowed and respiration will be still carried on. Indeed, in 



