SPINAL CORD AS A PATH OF CONDUCTION. 175 



duction 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 the contiguous 

 portions of the white. In these cases a frequent symptom is 

 what is known as the dissociation of sensations; the patient 

 loses, in certain regions, the sensations of pain and temperature 

 (analgesia and thermo-anesthesia), but preserves that of pressure 

 (touch). Facts of this kind ^indicate that the paths of conduc- 

 tion 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 (posterior column) soon after their 

 entrance, and the path is continued upward by tract cells whose 

 axons enter the proper fasciculi in the anterolateral funiculi,* 

 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 has prevailed. This 

 sense is not lost or, at least, is rarely lost in cases of syringomyelia 

 in which the other cutaneous senses are affected. On the other 

 hand, the posterior funiculi, as we have seen, may be completely 

 sectioned in lower animals without destroying the sense of touch 

 and in the case of man extensive pathological lesions of the same 

 funiculi 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 association fibers of the posterior funiculi, and by the short 

 association fibers of the lateral funiculi. 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 funiculi, by means of tract 

 cells and short association tracts. The fact that in man the 

 clinical evidence seems to point to the posterior funiculi as a pos- 

 sible or, indeed, probable path for these fibers may serve to ex- 

 emplify the fact that in these matters the various mammalia 

 differ more or less according to the degree of their development. 

 It seems possible that, so far as man is concerned, an explanation 

 of the difference of opinion regarding the spinal paths of the sense 

 of touch is found in the distinction made by Head and Thompson f 

 between tactile discrimination and cutaneous sensibility to touch. 

 By the former is meant the ability to discriminate between two 

 stimuli applied simultaneously to the skin at a certain distance 

 apart, by the latter, the ability to perceive and locate accurately 

 a light pressure stimulus applied to the skin. These two forms of 



* For discussion, see Bertholet, "Le Nevraxe," 1906, vii., 283, for the 

 lower animals; Head and Thompson, "Brain," 1906, p. 537, and Thompson, 

 "Lancet," 1909, for man. 



f Head and Thompson, "Brain," 1906; also Saunders, "Brain," 36, 166, 1913. 



