308 FUNCTIONS OF THE NERVOUS SYSTEM. 



Cord ; as the following experiments demonstrate. " Two Rabbits were taken ; 

 from one the head was removed ; from the other also the head was removed, 

 and the spinal marrow was cautiously destroyed with a sharp instrument : the 

 limbs of the former retained a certain degree of firmness and elasticity; 

 those of the second were perfectly lax." Again : "The limbs and tail of a 

 decapitated Turtle possessed a certain degree of firmness or tone, recoiled on 

 being drawn from their position, and moved with energy on the application of 

 a stimulus. On withdrawing the spinal marrow gently out of its canal, all 

 these phenomena ceased. The limbs were no longer obedient to stimuli, and 

 became perfectly flaccid, having lost all their resilience. The sphincter lost 

 its circular form and contracted state, becoming lax, flaccid, and shapeless. 

 The tail was flaccid, and unmoved on the application of stimuli." It is further 

 remarked by Messrs. Todd and Bowman, that ' a decapitated frog will con- 

 tinue in the sitting posture through the influence of the spinal cord ; but im- 

 mediately this organ is removed, the limbs fall apart." 



399. This operation of the Spinal Cord is doubtless but a peculiar mani- 

 festation of its ordinary reflex function. We shall hereafter see (Section 5) 

 how much the influence of the will in producing the active contraction of a 

 muscle, is connected with sensations received from it; and it seems highly 

 probable, that the impression of the state of the muscle, conveyed by the 

 afferent fibres proceeding from it to the spinal cord, is sufficient to excite this 

 state of moderate tension through the motor nerves, arising from the latter. 

 Such a view derives probability from the fact, which must have fallen under 

 the observation of almost every one, that most reflex actions become increased 

 in energy if resistance is made to them. Of this we have familiar examples 

 in the action of the expulsor muscles, which operate in defecation, urination, 

 and parturition, if, when they are strongly excited, their efforts be opposed 

 by the will acting on the sphincters, or by mechanical means. Many forms 

 of convulsive movement exhibit the same tendency ; their violence being pro- 

 portional to the mechanical force used to restrain them.* Here it is evident 

 that the impression of resistance, conveyed to the Spinal Cord, is the source 

 of the increased energy of its motor influence ; from which we may fairly 

 infer that the moderate resistance, occasioned by the natural antagonism of the 

 muscles, is the source of their continued and moderate tension, whilst they 

 are under the influence of the Spinal Cord. This constant though gentle 

 action serves to keep up the nutrition of the muscles, which are paralyzed to 

 the will ; and this is still more completely maintained, if the portion of the 

 nervous centres, with which they remain connected, is so unduly irritable, 

 that the muscles are called into contraction upon the slightest excitation, and 

 are thus continually exhibiting twitchings, startings, or more powerful convuls- 

 ive movements. It is upon the state of nutrition of the muscles, that their 

 contractility depends, as will be shown hereafter ( 588) ; and hence the 

 Spinal Cord has an indirect influence upon this peculiar property, which is 

 more likely to be retained, when the muscle is still subject to the influence of 

 the Spinal Cord, though cut off from that of the Brain, than when it is com- 

 pletely paralyzed by the entire cessation of the influence of the nervous 

 centres. 



400. Pathological Phenomena. It would not be right to conclude this 

 account of the principal functions of the Spinal Cord, without adverting to 

 some of the leading Pathological applications of the physiological doctrines 



* Hence the absurdity of the common practice of endeavouring to prevent the move- 

 ments of the limbs and body, in convulsive paroxysms, by mechanical constraint Nothing 

 should be attempted but what is requisite to prevent the sullercr from doing himself an in- 

 jury- 



