36 CEREBRAL FORCES. [i. 



It is accustomed, for example, to decide as to the external 

 sensations which it feels through the terminating nerve-fibrils 

 of the left hand, which transmit the impressions they receive 

 to the brain, along the trunk of the nerve, that they take place 

 in virtue of external impression on the left hand. But if this 

 hand be amputated, and these terminating fibrils be altogether 

 removed, still every external impression made on the cut end 

 of the trunk of the nerve of the left arm, being likewise trans- 

 mitted to the brain, seems to come from the left hand, when, 

 from a want of attention, the accustomed method of estimating 

 the point of contact is adopted ; and the mind is only aware 

 from due observation, that its estimate is erroneous. This 

 case (in which there is no true external sensation from the left 

 hand) cannot prove that a true external sensation of an external 

 impression can reach the mind from a more distant spot than 

 the true point of impression of the nerve ; but simply that the 

 judgment may sometimes err respecting the external sensations, 

 which error is a defect of the judgment, and not of sensation. 

 In this way a thousand phenomena must be estimated, as when 

 a person thinks he has sensations in a lost limb, or when he 

 seeks the point of sensation in a broken limb, in a natural 

 direct line, and finds it in quite another place. 



39. External impressions may be made on many nerves at 

 the same time, and the mind can distinguish all and each of 

 the external sensations thence arising, although the impressions 

 come from the most distinct nerves into a common trunk (as 

 for example, the spinal cord), before they reach the brain, and 

 there form the material ideas of an external sensation. In 

 the same nerve, and, at the same time, different impressions 

 may be made, yet the mind accurately distinguishes them ; so 

 that every external impression on each point of a nerve takes 

 also an uninterrupted course to the brain, and can there form 

 the material sensation peculiar to itself, and distinct from all 

 others, without being confounded or mingled, either on its way 

 with other impressions ascending at the same time, along the 

 nerve, or with the material sensations which arise at the same 

 time in the brain. The reason of this is, that the terminating 

 fibrils ^hich receive the impressions run a distinct course to their 

 origin, and remain quite separate, however they may be united 

 with other fibrils to form an entire nerve, or, however the 



