ON THE ORGANIC FUNCTIONS. 313 



Nervous influence, which does not manifest itself in obvious movement, but in 

 altered performance of the intimate processes themselves ; showing itself in 

 the character of the organized tissue, or of the secreted product. The act 

 of Excretion is, like ingestion, entirely performed by muscular movement, 

 dependent upon Nervous agency. Now wherever such movements of distant 

 organs are usually performed in connection with each other, there is an obvious 

 channel for one kind of sympathy between them ; an interesting example of 

 this, is the contraction of the uterus which may be frequently made to occur, 

 when that organ is in a relaxed state at the conclusion of labour, by applying 

 suction or other irritation to the nipple. 



421. Sympathetic movements of this kind may be excited either through 

 the Cerebro-Spinal, or the Ganglionic systems ; and we shall be guided in our 

 determination of their channel in each particular case, by the distribution of 

 these systems respectively to the organ affected. The sympathetic movements 

 of the Muscles of Animal life ( 366) appear to be chiefly, if not entirely, 

 excited through the Cerebro-spinal system; whilst those of the contractile 

 tissues of the Viscera ( 375) are probably excited through nerves, which, 

 though connected with the Cerebro-spinal system, act under peculiar condi- 

 tions, and are commonly spoken of as forming part of the Sympathetic system. 

 It has been shown ( 200) that all the contractile organs which may be excited 

 through the Sympathetic or Visceral system of nerves, may also be made to 

 act by stimuli applied to the roots of the Spinal nerves ; but that each Cerebro- 

 Spinal fibre appears to pass through several Ganglia, before being distributed 

 to the organs which it supplies. Many speculations have been hazarded as 

 to the reasons why the Visceral nerves are destitute of sensibility ; and, at the 

 time when the Sympathetic was supposed to be merely an offset from the 

 Cerebro-Spinal system, it was imagined that the use of the ganglia upon the 

 roots of the spinal nerves was to "cut off sensation" from those concerned in 

 the " vital and involuntary motions." The influence of Bichat's ingenious 

 hypothesis, that the Sympathetic system is complete and independent, minis- 

 tering to the functions of Organic Life, as the Cerebro-Spinal does to those of 

 Animal Life for a time caused this idea to be abandoned. Since, however, 

 it has been anatomically proved, that a large portion of the filaments of the 

 visceral nerves are derived from the Spinal cord, this opinion has been revived 

 in a somewhat modified form.* Nevertheless the evidence in its support is 

 somewhat vague ; especially if the truth of the doctrine formerly urged, that 

 the Spinal Cord is not itself a centre of sensation, be admitted. For it is 

 only necessary to suppose, that the white fibres of the Sympathetic nerve 

 terminate in the true Spinal Cord, without proceeding to the Brain, to have 

 an explanation of the absence of sensory endowments in the organs to which 

 they are distributed, and of the complete removal of the muscles supplied by 

 their motor nerves, from voluntary control. That a few fibres, of which the 

 actions cannot be excited under ordinary circumstances, pass on to the Brain, 

 would seem probable from the fact of the sensibility of some parts, in disease, 

 which are totally insensible in their normal condition ; a fact in the explana- 

 tion of which, the hypothesis just alluded to affords no assistance. 



422. It appears, then, that it may be stated as a general proposition, that 

 all the evident movements which can be excited, by irritation applied to one part 

 of the body, in the contractile organs or tis'sues of another, are really effected 

 through the true Spinal Cord ; whether the contractile organ be a powerful 

 muscle, or a thin and feeble layer of fibres around a blood-vessel or duct. 

 Upon the reasons why the fibres of the Visceral nerves should be so peculiarly 



* See Dr. Alison on the Nerves of the Orbit; Edinb. Phil. Trans., vol. xv.; and Med 

 Gaz., vol. xxviii. p. 378. 



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