294: NERVOUS SYSTEM. 



the section upon the opposite side of the body. 'In an article 

 published in 1858, Brown-Sequard details very succinctly an 

 experiment showing this fact, though his first experiments 

 were made in 1849. 1 He denuded the cord in the lumbar 

 region in a vigorous dog, and made sections upon one side, 

 progressively deeper and deeper, from without inward. 

 When the section included about one-third of the lateral 

 half, the sensibility seemed slightly augmented upon the 

 opposite side. This section involved only a part of the lat- 

 eral white column and a small portion of the anterior cornu 

 of gray matter. When the section was extended so as to 

 involve about two-thirds of the lateral half, the sensibility 

 was notably diminished upon the opposite side. When the 

 section extended to the median line, the sensibility was very 

 much diminished ; and when it extended just beyond the 

 median line, it was entirely abolished upon the opposite 

 side. 2 These observations, and others of the same nature, 

 show conclusively that in the animals experimented upon, 

 at least, there is a decussation of the greatest part of the 

 sensory conductors in the cord itself. 



The course of the fibres in their decussation is indicated 

 by further experiments, which show that the sensitive fibres 

 from the posterior roots of the nerves " pass along the poste- 

 rior columns only a little way, and leave them to enter the 

 central gray matter." ' It is undoubtedly in this gray sub- 

 stance that they pass from one side to the other, probably 

 through the cell-prolongations. The fact that the fibres pass 

 in the cord a short distance before they decussate, and that 

 they pass downward as well as upward, is well shown by the 

 following experiment : 



" If we divide transversely a lateral half of the spinal 



1 See list of works, in the Journal de la ph^siologie, Paris, 1862, tome v., 

 p. 646, No. 44. 



2 BROWN-SEQUARD, Nouvelles recherches sur la physiologic de la moelle epinere. 

 Journal de la physiologie, Paris, 1858, tome L, p. 139, et seq. 



8 BROWN-SEQUARD, Physiology and Pathology of the Central Nervous System. 

 Philadelphia, 1860, p. 25. 



