312 niYSIOLOGY OF MUSCLES A^^D NERVES. 



11. Duplex Thansmissiox. Degeneration, Regeneration 

 AND Coalescence of a Bisected Nerve (p. 218). 



Duplex transmission has been shown in another way, 

 but the proof is not so trustworthy and clear as that gained 

 by the aid of negative variation. If nerves of the living 

 animal are bisected, a striking change occurs in a very short 

 time in the parts of the nerve-fibre below the point of scission. 

 The medullary sheath becomes crinkled, and the excitability 

 is lost. If, however, the cut surfaces are not too fur sepa- 

 rated, the nerve-fibres can coalesce, the lower ends again 

 become excitable, and the excitement can be ti-ansmitted 

 through the cicatrix thus formed in the nerve. On these 

 facts Bidder based an experiment, in which he tried to cause 

 a sensory nerve to coalesce with a motor nerve. The sen- 

 sory nerve of the tongue [JV. lingualis), a branch of the fifth 

 brain nerve, and the motor nerve of the tongue {N. hypo- 

 ylossus) cross each other below the tongue before they enter 

 the latter. If the two nerves are cut at the point where 

 they cross, and if the upper end of the sensory nerve, which 

 comes from the brain, is connected with the lower end of the 

 motor nerve, which enters the tongue, as much as possible 

 of the two other ends of the nerves being cut out, then the 

 two difierent nerves coalesce, so that after a time pulsations 

 may be caused in the muscles of the tongue by irritation 

 above the cicatrix, and indications of pain may be elicited 

 by irritation below the cicatrix. The proof that in this case 

 tlie excitement is transmitted downward in the upper sensory 

 nerve, upward in the lower motor nerve, would be unassail- 

 able if it could be shown that nerve-fibres of the one nerve 

 1 ave not grown through the cicatrix and entered into the 

 other nerve. This possibility, improbable as it is, cannot 

 be disproved. 



A recently published experiment of Paul Bert is founded 



