IRRITABILITY AND CONDUCTIVITY 181 



the connecting wire, should be inclosed in a 

 glass tube for insulation. 



Expose the sacral plexus in a brainless frog in 

 which the skin has been removed from the hind 

 limbs. Connect the preparation by means of a 

 copper wire with the earth through the gas or 

 water pipes. 



Touch the sacral nerves here and there with 

 the needle electrode, watching meanwhile the 

 sartorius muscle. 



Partial contractions will be seen in the sar- 

 torius, now of the inner, now the outer fibres, 

 according to the nerve fibres touched 

 by the needle. 



Stimulate the sartorius directly. 

 Only the fibres touched by the 

 needle contract. 



Evidently the excitation wave re- 

 mains limited both in the muscle 

 and the nerve to the fibres in which 



Stirtorius, lu SLcLiuS* 



The same Nerve Fibre may conduct Impulses 

 both Centripetally and Centrifugally. 1. The 

 nerve of the sartorius divides at the muscle, part 

 going to each half of the muscle (Fig. 43). 

 Microscopical examination shows that the divi- 

 sion is not simply a parting of individual nerve 

 fibres, but that each axis cylinder forks, one 



