REFLEX ACTION WITHOUT SENSATION. 377 



but loss of sensation also. Further, in several cases of this 

 kind, in which the injury was confined to a small portion of 

 the cord, and the part below was not seriously disturbed, it 

 has been noticed that motions may be excited in the limbs by 

 stimuli applied directly to them, as, for instance, by tickling 

 the sole of the foot, pinching the skin, or applying a hot plate 

 to its surface ; and this without the least sensation, on the 

 part of the patient, either of the cause of the movement, or 

 of the movement itself; the nervous communication, which 

 would otherwise have conveyed the impression to the brain 

 and there given rise to sensation, being interrupted in the 

 spinal cord. 



469. By such cases, then, it appears to be clearly proved, 

 that the actions performed by the Spinal Cord, when the 

 Brain has been removed, or its power destroyed, or its com- 

 munication with the part cut-off, do not depend upon Sensa- 

 tion; but upon a property peculiar to the Spinal Cord, by 

 which impressions, made upon certain parts, necessarily excite 

 motions of an automatic character. By other experiments it 

 has been shown to be necessary for the exercise of this Reflex 

 function (as it has been termed), that an impression should be 

 conveyed by one set of nervous fibres, from the point where 

 the stimulus is applied, to the Spinal Cord ; and that a motor 

 impulse, conveyed by another set of filaments, should issue 

 from the Cord to the muscles. The excitor and motor fila- 

 ments distributed to any part are commonly bound up in 

 the same trunk, and are connected with the same part of the 

 Spinal Cord; so that, if this portion or segment be com- 

 pletely separated from the rest, it may still execute the reflex 

 movements of the parts to which its nerves are distributed ; 

 just as a single segment of a Centipede will continue to 

 move its legs, provided its own ganglion be entire ( 443). 



470. But in other instances it happens that we can more 

 clearly distinguish between the excitor and the motor nerves, 

 from their being distributed separately, and being connected 

 with distinct portions of the spinal cord. Thus in the act of 

 deglutition ( 195), the chief excitor nerve is the glosso-pha- 

 ryngeal ( 459) ; this conveys the impression made by the 

 contact of food with the pharynx, to the Medulla Oblongata ; 

 but it does not convey the motor influence to the muscles, 

 this being accomplished by branches of another nerve, the 



