312 rilYHOI.OGY 01- MUSCLES AM' M-.KVK*. 



11. l>riM.i:x TRANSMISSION. |M-:..I;\I:I;ATION, 



\-.n I COALESCENCE OF A ]>lsi;( Ti;i> Xi:i;\ i: (l. L'lS). 



Duplex transmission has been shown in another way, 



but the proof is not 8O trustworthy ami cleir as tlial gained 

 by the ai<l of negative variation. If nerves of the living 

 animal arr bisected, a striking change ocours in a very short 

 time in the parts of the nerve -Jil>re below the point of scission. 

 The nit'diillary sheath becomes crinkled, and* the excitability 

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

 rated, the nerv, '-fibres r ;, u coalesce, the lower cuds again 

 become exciialile, and the excitement can be transmitted 

 through the cicatiix thus formed in the nerve. ( >n these 

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

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

 sory ner\c of the tongue (.V. i< in/inilix}, a branch of the fifth 

 brain nerve, and the motor nerve of tin- tongue (.V. Itjpo- 

 i/li'ssus) 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 eud of the sensory nerve, which 

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

 mot )r nerve, \\hich enters the tongue, as much as possible 

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

 two dilleivnt nerves coalesce, SO that after a time pulsations 

 may be caused in the muscles of the tongue by in Station 

 above the cicatrix, and indications of pain may be elicited 

 by irritation below the cicatiix. The proof that in this ca-e 

 the excitement is transmitted downward in the upper .sensoi y 

 i.erve, up\\ard in the lower motor nerve, would lie unassail- 

 able if it could be sho\\ ii that nerve fibres of the one nerve 

 lave not grown through the cicatiix and entered into the 

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

 be di <pro\ed. 



A recently published experiment of 1'aul Mert is founded 



