804 CUTANEOUS SENSATIONS. [BOOK in. 



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 hemisec- 

 tion satisfactory proof of any such marked loss on the crossed 

 side ; they find on the contrary that impulses giving rise to sen- 

 sations of touch and of temperature, as well as those concerned 

 in the muscular sense pass up the same side, while those giving 

 rise to pain seem to pass up both sides, that is to say probably 

 travel along the grey matter. 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. 



508. Turning now to man we find that clinical experience 

 shews that in him the integrity of the cerebral hemispheres, 

 and of the connection of the hemispheres with the rest of the 

 central nervous system, is essential to the full development of 

 sensations ; and that in this respect each hemisphere is related 

 to the crossed side of the body. A very common form of paraly- 

 sis or 'stroke ' is that due to a lesion of some part of one hemi- 

 sphere (the exact position of the lesion need not concern us 

 now), frequently caused by rupture of a blood vessel, in which 

 the patient loses all power of voluntary movement and all sensa- 

 tions on the crossed side of his body (including the face) ; he 

 is said to be suffering from hemiplegia, 'one sided stroke.' 

 Not only do voluntary impulses fail to reach the muscles of the 

 affected side, but sensory impulses, such as those which, started 

 for instance in the skin, would under normal conditions lead to 

 sensations of touch, of heat or cold, or of pain, fail to effect con- 

 sciousness, when they originate on the affected side ; the patient 

 cannot on that side feel a rough surface, or a hot body, or the 

 prick of a pin. The same is true when the loss of sensation is 

 not complete, but partial. 



Further, though perhaps anatomical considerations would 

 lead us to expect that a great deal of the crossing took place in 

 the spinal bulb, clinical histories moreover agree, at least to 

 large extent, in shewing that much takes place in the cord, so 

 that when the lesion is confined to one half of the cord, the sensa- 

 tions affected in the parts below the level of the lesion are chiefly 

 or even exclusively those of the crossed side. But there is not 

 entire accordance among observers, especially as to the crossing 

 being complete. And with regard to the muscular sense there 

 is a distinct conflict of opinion ; the majority of cases seem to 

 shew that in unilateral disease or injury to the cord, the muscu- 

 lar sense in company with the voluntary movements, fails on the 



