290 LECTURE XII. 



is a point to which more recent researches have been 

 principally directed by Rudolph Wagner, inasmuch as 

 this inquirer instituted investigations into the distribu- 

 tion of the nerves in the electrical organ of fishes, and 

 in so doing gave the chief impulse to the doctrine of the 

 ramification of nerve-fibres. Up to that time nerves had 

 been regarded as continuous, single tubes, which re- 

 mained single throughout the whole of their course from 

 a nervous centre to their termination. At present we 

 know that nerves are distributed like vessels. Now see- 

 ing that nerve-fibres directly divide, usually dichoto- 

 mously, and their branches again divide and subdivide, 

 extremely abundant ramifications may in this way in 

 time arise, the import of which is extremely different, 

 according as the nerve is motor or sensitive, and either 

 collects impressions from, or diffuses motor impulses to, 

 a considerable extent of surface. A truly marvellous 

 instance has lately come to our knowledge in the electri- 

 cal nerve of the electrical silurus (malapterurus), which 

 has become so celebrated by the interesting experiments 

 of Dubois-Reymond. Here Bilharz has shown that the 

 nerve which supplies the electrical organ is in the first in- 

 stance only a single microscopical primitive fibre, which 

 keeps continually dividing until it finally resolves itself 

 into an enormously great number of ramifications which 

 spread themselves out upon the electrical organ. Here 

 therefore the nervous influence must all at once diffuse 

 itself from one point over the whole extent of the elec- 

 trical plates. 



In man we are still in want of distinct evidence with 

 regard to this question, because the immense distances, 

 over which individual nerves extend, render it almost 

 impossible to follow any single given primitive fibres 

 from their central origin to their extreme peripheral ter- 

 mination. But it is not at all improbable that in man 



