174 PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



the conduction as far as the medulla is not known (Fig. 78a). Re- 

 garding the path for the touch impulses a singular amount of un- 

 certainty has prevailed. This sense is not lost or, at least, is 

 rarely lost in cases of syringomyeha in which the other cutaneous 

 senses are affected. On the other hand, the posterior funicuH, as 

 we have seen, may be completely sectioned in lower animals with- 

 out destroying the sense of touch, and in the case of man extensive 

 pathological lesions of the same funicuh 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 poste- 

 rior funicuh, and by the short association fibers of the lateral fu- 

 nicuh. Such a view receives httle 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 



Fig. 78a. — Schema to indicate the general path taken by the fibers of pain, temperature, 

 and pressure, showing the crossed connection with the posterior root fibers. The path is indi- 

 cated only for one side. 



funiculi, by means of tract cells and short association tracts. The 

 fact that in man the chnical evidence seems to point to the poste- 

 rior funicuh as a possible or, indeed, probable path for these fibers 

 may serve to exemphfy the fact that in these matters the various 

 mammalia differ more or less according to the degree of their de- 

 velopment. 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 t between tactile discrimination and cutaneous sensi- 

 bility to touch. By the former is meant the abihty to discriminate 

 between two stimuli applied simultaneously to the skin at a certain 

 distance apart ; by the latter, the ability to perceive and locate ac- 

 curately a light pressure stimulus apphed to the skin. These two 



* Head and Thompson, "Brain," 1906: also Saunder's, "Brain," 36, 166, 

 1913. 



