CHAP, ii.] THE BRAIN. 1101 



ment we have evidence that under normal conditions 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 sensations, the interpretation of these signs 

 is beset with fallacies. Some observers have found that a hemi- 

 section (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 grey 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. 



683. The clinical histories of diseases of the spinal cord in 

 man bring to light in a fairly clear manner a fact of some import- 

 ance, namely, that the several impulses which form the bases of 

 the several kinds of sensations, of touch, heat, cold, and pain, and 

 of the muscular sense, are transmitted along the cord in different 

 ways and presumably by different structures. 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 

 impaired, 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 has 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 farther 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 shewing 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 

 sensation, are transmitted in different ways and follow different 

 "paths" along the spinal cord. 



