CUTANEOUS AND SOME OTHER SENSATIONS. 711 



stricter tone must influence the peripheral development of sensory im- 

 pulses. 



In these experiments, as in those on voluntary movements, it is most 

 important to distinguish between immediate or temporary and more lasting 

 effects ; and observers have found that the loss of sensation following a 

 hemisection of the cord, like the loss of voluntary movement, is temporary 

 only, and eventually disappears, though the recovery is slower and less 

 complete than is the case with movements. As with voluntary movement 

 ( 576) so with sensation, recovery, though less complete than that of 

 movement, is possible when a hemisection on one side has been at a later 

 date followed by a hemisection on the other side. We may, therefore, 

 repeat in reference to sensations the remarks which we made in reference 

 to movement. There is, however, an important difference between the two 

 cases : in respect to movement we have evidence that under normal condi- 

 tions the pyramidal tract plays an important part and that any other path 

 for volitional impulses is more or less an alternative one, whereas in respect 

 to sensation we have no anatomical or other distinct proof of any such 

 normal path. 



The experiments on monkeys are in like manner neither accordant nor 

 decisive ; and even in these animals with their more varied signs of sensa- 

 tions, the interpretation of these signs is beset with fallacies. Some observ- 

 ers have found that a hemisection (in the thoracic region) produced loss 

 of sensation on the crossed side, accompanied by little or no loss on the 

 same side ; other observers again have failed to obtain after a hemisection 

 satisfactory proof of any such marked loss on the crossed side. Further, large 

 portions of the lateral column, the more internal parts adjacent to the gray 

 matter being left, have been removed without any very obvious and certainly 

 without any lasting defects of sensation on the one side or on the other. 



595. The clinical histories of diseases of the spinal cord in man bring 

 to light in a fairly clear manner a fact of some importance, namely, that 

 the several impulses which form the bases of the several kinds of sensa- 

 tions, of touch, heat, cold, and pain, and of the muscular sense, are trans- 

 mitted along the cord in different ways and presumably by different struc- 

 tures, for disease may impair one of these sensations and leave the others 

 intact. Thus cases of spinal disease are recorded, in which on one side of 

 the body or in one limb ordinary tactile sensations seemed to be little im- 

 paired, and yet sensations of pain were absent ; when a needle was thrust 

 into the skin no pain was felt, though the patient was aware that the needle 

 had been pressed upon the skin at a particular spot ; and conversely, in 

 other cases pain has been felt upon the insertion of a needle, though mere 

 contact with or pressure on the skin could not be appreciated. Again, 

 cases are recorded in which the skin was sensitive to touch or pain, but not 

 to variations of temperature ; it is further stated that cases have been met 

 with in which cold could be appreciated, but not heat, and vice versa; and 

 there are some facts which point to sensations of pain being more closely 

 associated with those of heat, and tactile sensations with those of cold, than 

 those of pain with those of touch or those of heat with those of cold. Cases 

 of spinal disease are also recorded in which the muscular sense appeared to 

 be affected apart from other sensations. We shall return to these matters 

 later on in dealing with the senses ; we refer to them now simply as show^ 

 ing that disease, limited as far as can be ascertained to the spinal cord, may 

 affect the several sensations separately, and therefore as suggesting that the 

 several kinds of impulses, forming the bases of the several kinds of sensa- 

 tions, are transmitted in different ways and follow different "paths" along 

 the spinal cord. 



