166 PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



ture (analgesia and thermo-anesthesia), 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 tempera- 

 ture, 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 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. But the number of such neurons concerned in the con- 

 duction 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 im- 

 pulses may be conveyed up the cord by several paths: by the 

 long association fibers of the posterior columns and by the short 

 association fibers of the lateral columns. Such a view receives no- 

 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 evi- 

 dence 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 may be that in man long 

 paths for the touch fibers, by way of the posterior column, have 

 been acquired in part. 



The Homolateral or Contralateral Conduction of the 

 Cutaneous Impulses. Great interest, from the medical side, 

 has been shown in the question of the crossed or uncrossed con- 

 duction of the cutaneous impulses in the cord. The matter is 

 naturally one of importance in diagnosis. In human beings it 

 was pointed out by Brown-Sequardf that unilateral lesions of the 

 cord are followed by muscular paralysis below on the same side 

 and loss of cutaneous sensibility on the opposite side. This syn- 

 drome has been held clinically to establish the diagnosis of a uni- 

 lateral lesion, and has led to the view that, while the conduction 

 of the motor impulses is homolateral, that of the sensory impulses 

 is contralateral. Experimental work on lower animals, on the con- 



* Oppenheim, "Archiv f. Physiologic," 1899, suppl. volume, 1. 



f Brown-Se-quard, "Journal de Physiologie," 6, 124, 232, 581, 1863. 



