176 PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



cutaneous touch sensations are mediated according to these authors 

 by separate systems of fibers. As the result of a spinal lesion the 

 power of discrimination may be lost over a given area of skin 

 which otherwise is completely sensitive to all cutaneous stimuli. 

 They find that the fibers of tactile discrimination travel up the 

 cord uncrossed in the posterior funiculi, together with the fibers 

 of muscle sense that is, the fibers which give us a sense of posi- 

 tion and movement of the limbs. The fibers of cutaneous touch 

 sensations in general, on the contrary, cross to the other side be- 

 fore reaching the medulla, and pass upward in the anterolateral 

 ground-bundles. 



Homolateral and Contralateral Conduction of the Cutaneous 

 Impulses. Great interest, from the medical side, has been shown 

 in the question of the crossed or uncrossed conduction 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-Sequard* 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 syndrome 

 has been held clinically to establish the diagnosis of a unilateral 

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

 motor impulses in the cord is homolateral, that of the cutaneous 

 sensory impulses is contralateral. Experimental work on lower 

 animals, on the contrary, has not supported this view. While 

 results in this direction have varied, as would be expected from 

 the intrinsic difficulties connected with the interpretation of 

 the sensations of an animal, the general outcome has been to 

 show that the sensory conduction is bilateral, but mainly on 

 the same side. That is, if the cord is cut on one side only (hemi- 

 sected) in the thoracic region, the cutaneous sensibility of the parts 

 below the lesion is impaired upon the same side, but not com- 

 pletely abolished, showing that some crossing has taken place, f 

 In fact, it is stated that pain sensations in the lower animals are 

 not abolished by a double hemisection, J that is to say, by a hemi- 

 section below, in the thoracic cord for example, on one side, and a 

 hemisection above, cervical cord, on the other side. That the 

 pain impulses get through to the brain under this condition would 

 seem to imply that they are conveyed either diffusely through the 

 central gray matter, or that they cross a number of times from one 

 side to the other. In man the evidence from the clinical side, as 

 far as it goes, indicates that the paths for touch, pain, and tempera- 

 ture are more specialized than in the lower mammals, so that the 

 results obtained from experiments upon the latter must be used 



* Brown-Sequard, "Journal de Physiologie," 6, 124, 232, 581, 1863. 

 t Mott, "Brain," 1895, 1, and Bertholet, "Le Nevraxe," 1906, vii., 283. 

 j Karplus and Kreidl, "Pfliiger's Archiv," 158, 275, 1914. 



