SPINAL COED 165 



white commissure to the opposite side of the cord and come to 

 lie on the lateral margin just ventral to the direct cerebellar 

 tract. They may be termed the ventro-spinal eerebellap tract, 

 and they too pass to the cerebellum, but by a different route 

 from those of the direct tract (see p. 177) (fig. 82, 3 and C). 



4. The fourth set of fibres form synapses with the cells in 

 the dorsal horn. From these, axons cross the ventral white 

 commissure to the opposite side of the cord, and have been 

 traced headwards to the posterior part of the thalamus opticus. 

 They may thus be called the spino-thalamie tract. They seem 

 to run in two groups: (1) Those concerned with the sensa- 

 tions of pain, of heat and of cold cross near their point of entry 

 and take up a position in close association with those of the 

 ascending ventro-lateral cerebellar tract (fig. 82, D). (2) Those 

 concerned with the tactile sense, whether of light touch or of 

 pressure, run for a short distance up the dorsal columns, then 

 form synapses. The fibres from these cross at a higher level than 

 the last, and when they have crossed take up a position on the 

 ventral margin of the cord (fig. 82, E). 



As regards the side of the cord on which these fibres lie as 

 they course upwards to the brain, it has been demonstrated, 

 by section of one-half of the cord, that sensations of pain, 

 temperature, and to a less extent of touch, are lost on the 

 opposite side below the point of section, and that the kin- 

 sesthetic sense and partly the tactile sense are lost on the 

 same side. These symptoms are explained by fig. 81. 



The position of the fibres in the different columns of the cord 

 has been determined by studying the results of section of the 

 different columns and by following out the degenerations which 

 result. 



The degeneration method, or Wallerian method, is based 

 upon the fact, that nerve fibres separated from their cell die 

 and degenerate (see p. 85). These degenerations may be demon- 

 strated when recent by Marchi's method of staining, which 

 depends upon the fact that, while the white sheath of normal 

 fibres is not stained black when the tissue is placed in a 

 solution of chrome salt with osmic acid, it is so stained when 

 it begins to degenerate (p. 85). When, at a later period, the 

 white sheaths have entirely disappeared, the degeneration is 

 best demonstrated by Weigert's method of staining the white 



