CHAPTER X 

 Conduction in Nerve 



Conduction of nerve impulses may take place in both directions : 

 Kiihne's experiment. Remove the gracilis with part of its entering 

 nerve ; lay it on a glass plate, with its inner surface uppermost. The 

 nerve is seen to give branches upwards and downwards ; as a matter 

 of fact each nerve fibre divides into two branches, one for the upper 

 and the other for the lower part of the muscle, which has a tendinous 

 intersection obliquely across its middle. The middle part of the 

 muscle can be entirely cut through here without injuring these nerves, 

 and the two parts of the muscle will then only be united by the 

 forked nerves. 



If the ends of the nerves in either of the pieces of the muscle are 

 stimulated, whether electrically, osmotically (salt), or mechanically 

 (by snipping with scissors), both pieces contract. 



Rate of transmission of nerve impulse. Make a nerve-muscle 

 preparation in the usual way ; fix it upon the myograph, and lay the 

 nerve out upon two pairs of electrodes, one placed as near the muscle 

 as possible, the other close to the vertebral column. With a large 

 frog 5 centimetres (nearly 2 inches) will intervene between the two. 

 Place a commutator without cross wires in the secondary circuit, and 

 arrange so that by moving the bridge of the commutator the induction 

 shocks can be switched on to one or other pair of electrodes. The 

 drum is included in the primary circuit, and a short-circuit key in the 

 secondary (Fig. 42). 



Two muscle curves are now successively taken with a fast rate of 

 cylinder and a maximal stimulus. The stimulus is applied to the nerve, 

 first, close to the muscle, and, second, close to the vertebral column. 

 The muscle curves are both taken in exactly the same way, and with 

 exactly the same precautions as to the use of the stop, etc., detailed 

 in Chapter III., and both curves are to be traced upon the one abscissa, 

 a time tracing being written beneath this. It will be found that the 

 curves are not quite coincident, but that one succeeds the other by a 

 very small interval. This interval represents the time occupied by 



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