1100 CUTANEOUS SENSATIONS. [BOOK m. 



brought to light by the experiment shew but little accord with 

 the anatomical programme. We have dwelt on it so long because 

 it is more or less illustrative of the many difficulties attending 

 the interpretation of experiments of this kind ; and it is in this 

 respect all the more valuable because the actual experimental 

 results are sharp and clear. We may pass over more rapidly the 

 numerous experiments on the lower mammals, such as rabbits 

 and dogs, in which other indications of sensation have been made 

 use of, chiefly those which are the signs of painful sensations ; these 

 have been carried out in various regions of the cord, but chiefly 

 in the thoracic region, and in them a like uncertainty of inter- 

 pretation is farther increased by the want of exactness and 

 agreement in the results. 



If we content ourselves with making no distinction between 

 the different kinds of afferent impulses, and in the case of these 

 animals it would hardly be profitable to attempt to make a 

 distinction, we may say that the several experiments so far agree 

 that they point to the lateral columns as being the chief paths of 

 afferent, sensory, impulses, or to speak more exactly, to the 

 passage of these impulses being especially blocked by section of 

 the lateral columns. Some observers find that in the dog and 

 other lower mammals a section of the lateral column on one side, 

 or at least a hemisection of the cord, produces ' loss of sensa- 

 tion' on the opposite side greater than on the same side, or 

 confined to the opposite side, and even accompanied by an 

 exaltation of sensation, a hyperesthesia, on the same side. Other 

 observers again, and these certainly competent observers, find that, 

 in the dog, section of one side affects sensation on both sides, and 

 indeed chiefly on the same side. We may perhaps once more 

 repeat the warning how difficult is the quantitative and qualitative 

 determination of sensations in such an animal as the dog ; and 

 may remark that in all these cases of unilateral section the 

 increased blood supply due to failure of the normal vaso-con- 

 strictor tone must influence the peripheral development of 

 sensory impulses. 



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 ( 663) so with 

 seusation, 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 then made in reference to movement ; there is however an 

 important difference between the two cases ; in respect to move- 



