700 OF THE FUNCTIONS OF THE NERVOUS SYSTEM. 



state of the system, a certain degree of firmness, by their antagonism with each 

 other ; and if any set of muscles be completely paralyzed, the opposing muscles 

 will draw the part on which they act out of its position of repose ; as is well 

 seen in the distortion of the face which is characteristic of paralysis of the facial 

 nerve on one side. This condition has been designated as the tone of the 

 Muscles; but this term renders it liable to be confounded with their tonic 

 contraction ( 331), which is also concerned in maintaining their firmness, but 

 which is a manifestation of the simple contractility of their tissue, and is exhi- 

 bited alike by the striated and the non-striated forms of muscular fibre, but 

 more especially by the latter. On the other hand, the condition now alluded 

 to, which may perhaps be appropriately termed their tension, is the result of a 

 moderate though continued excitement of that contractility, through the nervous 

 centres. It has been proved by Dr. M. Hall that the Muscular Tension is not 

 dependent upon the influence of the Brain, but upon that of the Spinal Cord j 

 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." 1 It is further remarked, by Messrs. 

 Todd and Bowman, that " a decapitated frog will continue in the sitting posture 

 through the influence of the spinal cord ; but immediately this organ is removed, 

 the limbs fall apart." This operation of the Spinal Cord is doubtless but a 

 peculiar manifestation of its ordinary reflex function. We shall hereafter see 

 ( 750) 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 ob- 

 servation of almost every one, that most reflex actions become increased in 

 energy if resistance be 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 

 spasmodic contraction of 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. 3 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 porton of the nervous centres, with 



1 " Memoirs on the Nervous System," 1837, p. 93. 



2 Hence the absurdity of the common practice of endeavoring to prevent the movements 

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

 be attempted but what is requisite to prevent the sufferer from doing himself an injury. 



