16 I'HYSIOLOGY. 



situation and attachments, to be, by their contraction, capable 

 of moving most of the solid and fluid parts of the body. These 

 we name the MOVING EXTREMITIES of the nerves : they are 

 commonly named MOVING or MUSCULAR FIBRES. 



Note. That the muscular fibres are a continuation of the me- 

 dullary substance of the brain and nerves, has not been shewn by 

 the anatomists, nor universally admitted by the physiologists ; 

 but we now suppose it, and hope, afterwards, to render it suffi- 

 ciently probable. 



Are the ganglions of the nerves to be considered as a part of 

 the nervous system distinguished by a peculiar function ? " A 

 fifth part of the nervous system might be mentioned, viz. the 

 portions of the nerves formed into ganglions. It is ascertained 

 that they are a distinct part ; but my question is, Whether they 

 are to be distinguished by a peculiar function ? They may de- 

 serve to be considered even in that light as a distinct part; but 

 this is not so well ascertained ; and the present opinion is, that 

 their functions are only modifications of the common properties 

 of the nerves, without any distinct property or function." 



XXX. These several parts of the nervous system are every 

 where the same continuous medullary substance which we sup- 

 pose to be the vital solid of animals, so constituted in living 

 animals, and in living systems only, as to admit of motions 

 being readily propagated from any one part to every other part 

 of the nervous system, so long as the continuity and natural 

 living state of the medullary substance remains. 



Note. It is observed, that the compression of any part of 

 the medullary substance prevents the communication of motion 

 between the parts that lie on different sides of the part com- 

 pressed ; and it is probable there are other causes besides com- 

 pression, which may also affect the medullary substance, so as 

 to interrupt in it the communication of motion ; but they are 

 not distinctly known. " Cold may be one of them ; and putre- 

 faction^ or a peculiar matter arising from the putrid state, may 

 be another." In the mean time, we use the expression that a 

 nerve, or other portion of the nervous system is free, to denote 

 its being free not only from compression, but from every other 

 supposed cause interrupting the communication of motion. 



