574 FUNCTIONS OF THE CEREBRO -SPINAL NERVOUS SYSTEM. 



the spinal cord be destroyed. Lastly the occurrence of the negative oscilla- 

 tion of the current, that is to say the disappearance of the normal current 

 which exists in both sensory and motor nerves, on excitation of these nerves 

 by any stimulus, affords an additional proof that the particles of nerves can 

 conduct in either direction. In the same way, although as a rule sensory 

 impressions are only conducted towards the new centres, yet some evidence 

 has been obtained to show that they may conduct in an opposite direction. 

 Thus, MM. Philippeaux and Vulpian 1 divided the hypoglossal and lingual 

 nerves, which are conveniently placed for the experiment, and applied the 

 peripheric extremity of the hypoglossal to the centric extremity of the lin- 

 gualis. They found that in a few weeks union took place, and that the muscles 

 of the tongue might be excited to contract by an electrical current applied 

 to the lingualis or sensory nerve. MM. Philippeaux and Vulpian drew the 

 conclusion that when the properties of the hypoglossal are abolished by sec- 

 tion the lingualis after the lapse of some time acquires motor fibres it did 

 not previously possess. It is to be observed, however, that although the 

 fibres can thus conduct an electrical stimulus there is total loss of voluntary 

 control over the lingual muscles, and if the operation be performed on both 

 sides the animal is rendered permanently incapable of protruding his tongue. 

 In Bidder's experiments, 2 microscopical examination of the nerves showed 

 that the peripheric extremity of the lingualis consisted exclusively of nerve- 

 fibres which had undergone fatty degeneration, whilst in the peripheric por- 

 tion of the hypoglossal which had united with the centric of the lingualis, 

 the greater number of the fibres presented their normal characters. And 

 this accorded with the fact that, when the nerve was cut during life, the 

 animal gave marked indication of pain, and the same side of the tongue was 

 convulsed. 



IV. When the whole trunk of a motor nerve is irritated, all the muscles 

 which it supplies are caused to contract. This contraction evidently results 

 from the similarity between the effect of an artificial stimulus applied to the 

 trunk in its course, and that of the change in the central organs by which 

 the motor influence is ordinarily propagated. But when only a part of the 

 trunk or a branch is irritated, the contraction is usually confined to the mus- 

 cles which receive their nervous fibres from it ; in this instance, as in the 

 other, there is no lateral communication between the fibrils. 



464. Determination of the Functions of Nerves. Various methods of deter- 

 mining the functions of particular nerves present themselves to the Physio- 

 logical inquirer. One source of evidence is drawn from their peripheral 

 distribution. For example, if a nervous trunk is found to lose itself entirely 

 in the substance of Muscles, it may be inferred to be chiefly, if not entirely, 

 motor or efferent. In this manner Willis long ago determined that the Third, 

 Fourth, Sixth, Portio dura of the Seventh (or Facial), and Ninth cranial 

 nerves, are almost entirely subservient to muscular movement ; and the same 

 had been observed of the fibres proceeding from the small root of the Fifth 

 pair, before Sir C. Bell experimentally determined the double function of that 

 division of the nerve into which alone it enters. Again, where a nerve passes 

 through the muscles, with little or no ramification among them, and proceeds 

 to a Cutaneous or Mucous surface on which its branches are minutely dis- 

 tributed, there is equal reason to believe that it is of a sensory or rather of 

 an afferent character. In this manner Willis came to the conclusion, that 

 the Fifth pair of cranial nerves differs from those previously mentioned, in 



1 MM. Pliilippoaux and Vulpian, Cumptes Rendus, 1860, t. ii, p. 363, mid idem, t. 

 iii, p. 8 Archiv. Gen. de Modi-cine, July, lHfJ'5, p. 122 See also Gluge iuid Thior- 

 IIOM-. Brown-S6quard'8 Journal de la Physiologie, 1859, t. ii, p. 686. 



2 Rcichcrt's Archiv, 1805, p 246. 



