SPINAL CORD AS A PATH OF CONDUCTION. 167 



The Spinal Paths for the Cutaneous Senses (Touch, Pain, 

 and Temperature). From the facts stated in the last two para- 

 graphs it would seem probable that the spinal paths for touch, 

 pain, and temperature must be along the short association tracts 

 of the ground bundles of the lateral and anterior columns. There 

 is evidence from the clinical side that the paths of conduction for 

 these senses are separate. In the pathological condition known 

 as syringomyelia cavities are formed in the cord affecting chiefly 

 the central gray matter and ^he contiguous portions of the white. 

 In these cases a frequent symptom is what is known as the dis- 

 sociation of sensations; the patient loses, in certain regions, the 

 sensations of pain and temperature (analgesia and thermo-anes- 

 thesia), but preserves that of pressure (touch). Facts of this kind 

 indicate that the paths of conduction for touch are separate from 

 those for pain and temperature, but little that is positive is known 

 regarding the exact location of these paths. The fibers of pain 

 and temperature probably end in the gray matter of the cord (pos- 

 terior horn) soon after their entrance, and the path is continued 

 upward by tract cells whose axons enter the ground bundles in the 

 lateral or anterolateral columns, most probably in the lateral col- 

 umns, so far at least as the lower animals are concerned,* but 

 the number of such neurons concerned in the conduction as far as 

 the medulla is not known. Regarding the path for the touch 

 impulses a singular amount of uncertainty prevails. This sense 

 is not lost in cases of syringomyelia in which the other cutaneous 

 senses are affected. On the other hand, the posterior columns, 

 as we have seen, may be completely sectioned in lower animals 

 without destroying or, indeed, affecting the sense of touch, and 

 in the case of man extensive pathological lesions of the same col- 

 umns are reported in which the sense of touch was not lost. Some 

 authors, therefore, have been led to believe that the touch impulses 

 may be conveyed up the cord by several paths: by the long asso- 

 ciation fibers of the posterior columns and by the short association 

 fibers of the lateral columns. Such a view receives little support 

 from the experimental work on the lower mammals. In these 

 animals the evidence tends to show that the conduction is by way 

 of the lateral or anterolateral columns, by means of tract cells and 

 short association tracts. The fact that in man the clinical evidence 

 seems to point to the posterior columns as a possible or indeed 

 probable path for these fibers may serve to exemplify the fact that 

 in these matters the various mammalia differ more or less according 

 to the degree of their development. It seems possible also that 

 some confusion may have resulted from a failure to differentiate 

 between true cutaneous touch (pressure) sensations and those 

 * For recent discussion see Bertholet, Le Nevraxe, 1906, vii.. 283. 



