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XXI. On the Functions of some parts of the Brain, and on the relations between the 

 Brain and Nerves of Motion and Sensation. By Sir Charles Bell, F.R.S. 



Received March 3, — Read May 15, 1834. 



J. HE difficulties which attend the investigation of the structure and functions of the 

 brain are shown by the ineffective labours of two thousand years ; and the first en- 

 deavour of the author is to remove the idea of presumption that attaches to the very 

 title of this paper. Perhaps the enumeration of some of the sources of error which 

 have retarded discovery may be the best introduction and apology. 



The first impediment to success is in the nature of the inquiry, since extraordinary 

 and contradictory results must be expected from experimenting on an organ so fine 

 as that must be which ministers to sensibility and motion, and which is subject to 

 change on every impression conveyed through the senses. This remarkable suscep- 

 tibility is exemplified in what we often witness ; extraordinary results, such as violent 

 convulsions and excruciating pain, from causes which appear quite inadequate. For 

 example, the presence of a minute spicula of bone which has penetrated to the brain, 

 will at one time be attended with no consequence at all ; at another it will occasion 

 a deep coma, or loss both of sensibility and motion. Nay, symptoms apparently as 

 formidable will be produced by slight irritation on remote nerves. Seeing these con- 

 tradictory effects, is it reasonable to expect constant and satisfactory results from 

 experiments in which deep wounds are inflicted on the brain of animals, or portions 

 of it torn away ? 



Other circumstances evince the slight varieties in the causes which produce the 

 most extraordinary effects. Water in the brain, which has free access to all the ca- 

 vities of the brain, and which to all appearance both presses equally, and if it irritate 

 must irritate equally, will have the effect of rendering one side of the body paralytic 

 and of convulsing the other with incessant motion. 



Another source of error, especially to the experimenter on the brain, is the disturb- 

 ance of its circulation ; for the brain depends more directly than any other organ on 

 the condition of the circulation within it. We may see this in the provisions for the 

 free and equable supply of the blood within the head, as well as for its unimpeded 

 exit. Now by raising the skull, a necessary preliminary to most experiments on the 

 substance of the brain, there is an immediate disturbance of the circulation, which of 

 itself may be attended with insensibility or convulsions. 



The most frequent source of error, perhaps, is the obscurity which hangs over the 



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