EFFECTS OF WITHDRAWAL OF NERVOUS POWER. 449 



the wasting-away of the muscles which otherwise takes place ; 

 and thus we see that the preservation of this peculiar property 

 is dependent upon the due nutrition of the muscle, whilst the 

 loss of the property results from its want of nutrition, as we 

 find to be the case in regard to other tissues. Further, the 

 activity of the nutrition of muscles depends in great part 

 upon the use that is made of them ; and thus we find that 

 any set of muscles in continual employment undergoes a great 

 increase in size and vigour ; whilst those that are disused, 

 even though their nervous connexions remain entire, lose 

 their firmness and diminish in bulk, until, if the inaction be 

 continued long enough, almost all trace of proper muscular 

 substance disappears, and the contractility of the part is lost. 



588. But a muscle may be palsied by some change taking 

 place in the central organs, which shall prevent the nervous 

 influence from being excited there. Thus by an effusion of 

 blood in a certain part of the brain, the arm, leg, or the whole 

 of one side may be paralysed to the influence of the will. 

 But the muscles which are thus withdrawn from the power of 

 the will, may sometimes be moved by an emotional or instinctive 

 impulse, or by reflex action ; their connexion with the parts of 

 the nervous centres, in which these actions respectively origi- 

 nate, remaining unimpaired (Chap. x.). Thus a completely 

 paralytic arm has been seen to be violently shaken, when the 

 emotions of the patient were strongly excited by the approach 

 of a friend. The muscles of the shoulder, in a case of com- 

 plete paralysis of one side, were called into contraction in the 

 reflex movement of yawning ( 341). And the muscles of 

 the legs, when their communication with the brain, and 

 consequently the control of the will over them, has been 

 completely cut off", have been made to act energetically when 

 the feet were tickled, although the patient was not conscious 

 either of the irritation or of the motion. When the muscles 

 are thus aroused to occasional activity, their nutrition is not 

 so much impaired, and their contractility does not depart 

 nearly as completely as when they are thrown into entire 

 disuse by division of their nerves. 



589. Muscles are commonly divided into voluntary and 

 involuntary, according as they act in obedience to the will, 

 or are not under its dominion. But this is not a correct 

 division ; since, whilst nearly all the muscles of the body are 



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