48 THE HUMAN BRAIN. 



motion; and anatomy demonstrates that the course of these influ- 

 ences is ; in sensation, from the skin and sensories through the nerves 

 to the brain ; and in action or motion, from the brain through the 

 nerves to the muscles, bones, skin : in short, to the body as set in 

 motion. Furthermore investigation shows, that the course of the 

 same is, from the nervous fibres and fibrils, through the medullary 

 fibres of the brain, to the cortical or gray substances at its surface 

 and in other parts. What do we deduce from this known transit 

 of influence? Or what is the meaning of the ambiguous term, 

 influence? 



Two views have been current. On the one side it is maintained 

 that the fibres are solid, and that the influence is a vibration which 

 traverses the fibres in both directions. On the other hand, the in- 

 fluence is regarded as a real influxion, and the fibres are regarded as 

 conduits, permeated by a fluid. There is a third hypothesis, of a 

 gelatinous or other fluid in the nerves, which propagates forces by 

 waves or undulations, but does not itself move forward : but this is 

 only a subdivision of the doctrine of vibration. And there is a 

 fourth view — that we can. know anything about the matter. But 

 we do not yet know what can be known. In thus classifying opin- 

 ions we by no means intend to convey that they are held sharply by 

 any one at present: on this subject the state of most inquiring 

 minds is mixed; indeed the apathy felt of late respecting the con- 

 troversy is too profound to admit of distinctness of parties. 



I. If the fibres were solid, and traversed, not by a fluid, but by a 

 vibration or undulation, such vibration would be dissipated into the 

 surrounding parts, especially in the brain, where the fibres lie close 

 together. The softness and non-elasticity of all parts of the nervous 

 system seem unadapted to mere vibration being communicated, for 

 vibration depends upon tension, and the only condition of tension in 

 such a system lies in a movable fluid distending the fibres. And 

 when a nerve is tied, the sensation or motion which is supplied be- 

 comes arrested at once, which would not be the case if these de- 

 pended upon vibration. Certainly nothing can be conceived less 

 adapted than the brain and nerves, to the ordinate propagation of 

 electricity or any other imponderable, unless limited to a fluid vehicle. 

 The hypothetical currents of vibration, however, must be ordinate 



