ON THE MAMMALIAN NERVOUS SYSTEM. 



405 



they enter. It has been shown by the present experiments that, as far as the 

 nerve impulses aroused by electrical excitation of nerve fibres in the cord are con- 

 cerned, no such extensive crossing occurs in the dorsal or lumbar regions ; and the 

 experiments in Chapters IX. and X., on the relation of the cord to the lumbar nerves, 

 show that no such extensive crossing into the opposite lateral column occurs when the 

 impulses are generated in the entering nerves themselves. 



It is difficult to perform a satisfactory experiment on the influence of section of one 

 lateral column, since the extensive lesion alters the excitability of the posterior column 

 of the same side, and this interferes with the sharpness of the results. To avoid this 

 we made the experiment upon an animal (Cat 259)* in which thirty-four days pre- 

 viously the lateral column had been severed on the left side at the level of the 10th 

 dorsal vertebra. The cord was then divided and prepared in the dorsal and lumbar 

 regions, and the following results obtained : 



Average of lateral on side of section . 

 Average of lateral opposite to section 

 Average of posterior columns . 



Trace, 

 37, 

 51. 



The lateral column interruption with this intensity of stimulus, which from the 

 inexcitable condition of the cord was practically minimal, is thus sufficient to abso- 

 lutely block any transmission upwards of nerve impulses generated in those fibres of 

 that column which lie below in the excited lumbar region. 



* In this animal, just before the experiment, it was found that there was spastic paralysis in the left 

 hind limb with diminished sensibility. The knee jerks were equal and normally present. On micro- 

 scopical examination the lesion was found to have destroyed the lateral column of the left side, the 

 outer portion of the anterior column, and the dorsal two-fifths of the posterior column ; while, on the 

 right side, a portion of the posterior median was injured. Of descending degeneration there was 

 noted the posterior third of the left lateral and the median portion of the left anterior column. Of 

 ascending degeneration a section at the 5th dorsal showed degeneration in both postero-median 

 columns, extensive on the left side, but only few fibres in the centre of the right column. Left cerebellar 

 and antero-lateral tracts degenerated. 



