SENSOEY CONDUCTION IN THE SPINAL COKD. 287 



by experiments upon animals, in which these points are al- 

 ways difficult of determination. On the other hand, if every 

 portion of the cord be divided except the posterior columns, 

 sensibility is completely lost in the parts below the section. 

 The accuracy of these results cannot be called in question, 

 especially when controlled by experiments showing the con- 

 ducting properties of the gray substance of the cord ; and 

 they show that, whatever may be the functions of the poste- 

 rior white columns, they do not serve as conductors of sen- 

 sory impressions. 1 



The second question admits of an equally positive an- 

 swer from the results of experimental inquiry. If the entire 

 substance of the cord, except the posterior columns of white 

 matter, be divided transversely, as we have just seen, sensi- 

 bility is abolished in all parts below the section ; but, as we 

 have stated in treating of the transmission of motor stimu- 

 lus by the cord, voluntary motion is also destroyed. 11 Ex- 

 periments show, farthermore, that sensory impressions are 

 conveyed exclusively by the gray substance. " If the ante- 

 rior, the lateral, and the posterior columns of the spinal cord 



1 The experiments by Brown-Sequard, which have led to the above conclu- 

 sion, are of the most positive and satisfactory character (Physiology and Pathol- 

 ogy of the Central Nervous System, Philadelphia, 1860, p. 19), and have been 

 repeatedly confirmed by himself and other observers, among the most promi- 

 nent of whom are Yulpian and Philipeaux (VULPIAX, Systeme nerveux, Paris, 

 1866, p. 373). The most important experiments in opposkion are those of 

 Schiff, quoted and adopted by Longet, by which Longet endeavors to prove that 

 the posterior columns are conductors of the tactile sense (LONGET, Traite de 

 physiologic, Paris, 1869, tome iii., p. 353). In these experiments, the antero- 

 lateral columns were divided, and the animal was afterward enfeebled by a copi- 

 ous haemorrhage. Upon pinching the tail, the animal gave evidence of sensa- 

 tion, but suffered no pain, even when the sciatic nerve was bruised or torn. In 

 these observations, it was not shown that the entire gray substance was divided, 

 and the experiments after copious haemorrhage were certainly not made under 

 strictly physiological conditions. It is well known, also, that if a small portion 

 of gray matter be undivided, there is conduction of sensory impressions. In all 

 of Brown-Sequard's experiments, the exact h'mits of the sections of the cord 

 were ascertained by subsequent examination of the parts hardened in alcoboL 



8 See page 280. 



119 



SDICAL * 



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