156 FUNCTIONS OF THE NERVOUS SYSTEM. 



Brain or of the upper part of the Spinal Cord, but retain their power of reflex 

 action, (the nervous circle which operates through the Spinal Cord not being 

 interrupted) the contractility of the muscles is not diminished, but appears 

 to be sometimes even increased ; and he has suggested that this fact may be 

 made available as a means of diagnosis in obscure cases of paralysis. Thus, 

 in some cases of Paraplegia, the reflex actions may be excited ; in others they 

 cannot be. In the former, the disease must be in the dorsal or cervical portion 

 of the Spinal Cord, leaving its lumbar portion free to carry on the reflex actions, 

 though its connection with the brain is interrupted. In the latter, the disease 

 is probably within the lumbar vertebrae, involving that portion of the Spinal 

 Cord through which the reflex actions of the lower extremities are produced. 

 In like manner, in paralysis of a single arm or of one leg, if the reflex actions, 

 and the contractility of the muscles on the application of a direct stimulus 

 (such as galvanism), remain unimpaired, the cause is probably seated in. the 

 Brain ; whilst, if the tone of the muscles be completely lost, and no contraction 

 can be induced in them, the cause of the paralysis is probably somewhere in 

 the neighbourhood of the roots of the nerves of the part affected. There is no 

 good ground for believing, however, that the contractility of the muscles is 

 directly dependent on their connection with the Spinal Cord, a doctrine 

 which is inconsistent (as will be shown hereafter) with well-established facts. 

 It is well known that muscular structure requires, for its perfect nutrition, to 

 be kept in a state of functional activity. If the muscles of the leg, for example, 

 be disused for a long time, their nutrition is greatly impaired, and their con- 

 tractility is almost suspended ; even though they retain their connection with 

 the nervous centres, and the latter be in their normal condition. It is to be 

 expected, then, that, if a muscle be completely put out of the pale of nervous 

 influence, its nutrition should be speedily impaired, and its contractility alto- 

 gether lost ; but if the influence of the Brain only be withdrawn from it, and 

 its connection with the Spinal Cord be uninterrupted, it will be in a state of 

 continual action, by the operation of various reflected stimuli ; and this action 

 will be sufficient to maintain its nutrition, and to -prevent the loss of its con- 

 tractility (See Chap. V.). 



209. The fact, that the action of the Heart is in some degree under the 

 control of the Spinal Cord, has long been known. It is not a little curious 

 that, although its movements will continue regularly, after complete section of 

 all its nerves, any sudden and severe impression upon a large part of the 

 Nervous Centres, such as crushing the Brain or Spinal Cord, will produce 

 a great diminution in their frequency, or will even occasion their entire cessa- 

 tion, if the nervous connection be entire. It will be hereafter shown, that the 

 influence is partly communicated by the Par Vagum ; but it appears, from the 

 experiments of Valentin, that the Sympathetic is in part, as in the case of the 

 motions of the alimentary canal, the channel by which it is transmitted. He 

 found that, when the heart had ceased to beat, its contractions might be re- 

 newed by irritation of the roots of the Spinal Accessory nerve, and of the first 

 four Cervical nerves, and also of the first cervical ganglion of the Sympathetic. 

 He tjiinks that he has also witnessed distinct contractions of the thoracic aorta, 

 of the inferior cavity, and of the thoracic duct, upon irritation of the neigh- 

 bouring portion of the Sympathetic system, which evidently derives its whole 

 motor power from the Spinal Cord. The ductus choledocus has also been seen 

 by him to contract on irritation of the right splanchnic nerve. 



210. Lastly, we have to inquire how far the Reflex action of the Spinal 

 Cord is concerned in the locomotive actions of the lower extremities in Man. 

 It will be remembered that, in the Dytiscus whose head had been removed, 

 ( 146,) the stimulus of the contact of water immediately excited regular and 

 continued locomotive actions, which lasted for some time. So in the cases 



