WITH THE MICROSCOPE. 331 



short distance from the particles of tissue to be influenced. And it is 

 not known whether the influence is produced by the passage of a 

 continuous current varying in intensity, or by an interrupted current. 

 Nor is tkere more accord as to the origin of nerves in centres ; some 

 holding that the fibres invariably originate in cells, others that some 

 cells have no fibres at all connected with them. And of those who 

 admit the first proposition, some think the fibre comes from the 

 body of the cell, others trace it to the nucleus, while some profess to 

 have seen it emanating from the nucleolus. Or, again, concerning 

 the fibres, which unquestionably originate in nerve cells, it has been 

 stated that some pass into nerve fibres, while others have no special 

 relation to nerves at all. But it would occupy much more space 

 than it would be advantageous to devote to it, were I to attempt 

 to give even a very brief summary of all or even the most important 

 ef the conflicting opinions now entertained. And if I were to limit 

 myself to any one organ the reader would be equally bewildered by 

 the conflict of opinions, and by the multitude of assertions which 

 pass for statements of facts. And if he try to sift the evidence 

 adduced in favour of the views propounded, he will completely fail, 

 because they rest upon observations which for the most part he 

 will find himself unable to repeat. 



I shall venture to refer very briefly to some of the general con- 

 clusions I have myself arrived at in connection with the structure 

 and arrangement of nerves, by working according to the principles 

 enunciated in page 292. 



389. Of Plexuses anS Networks. Every one agrees that the 

 larger nerve trunks are in many instances so arranged as to form 

 plexuses or networks, to which various names have been assigned 

 by anatomists, according to their position, general form, origin, &c. ; 

 but it was supposed that in many cases nerves pursued an almost 

 direct course to their ultimate distribution, where they terminated 

 in free extremities, in cells, or by becoming continuous with the 

 texture they influenced. More careful observation has, however, 

 demonstrated that all nerves before they reach their finest ramifi- 

 cations form microscopic networks or plexuses, arranged upon the 

 same plan as the coarser networks above alluded to ; and I have 

 been able to demonstrate that the finest ramifications themselves 

 constitute a plexus or network, in which the component ultimate fibres 

 are arranged in much the same manner as the dark-bordered fibres 

 aJcrins into the formation of one of the ordinary plexuses. 



Careful observations upon the arrangement of particular nerve 

 plexuses in the same texture at different periods of development 

 have convinced me that the ultimate terminal plexus of the 



