MECHANICAL RESPONSE OF NERVE 



529 



Another interesting 



of the afferent or sensory nerves are in every way the same 

 as those of the efferent, or motor. The numerous records 

 already given are of the latter. For the demonstration of 

 the former I took the optical nerve of Opliiocephalus, and 

 recorded its responses to uniform electrical stimuli, on a 

 smoked surface. The following (fig. 324) is a photographic 

 reproduction of the record. Owing to sub-tonicity, the first 

 response is seen here to be abnormal positive. Successive 

 stimulation converts this, through diphasic, into normal 

 negative, in a manner exactly the same as has already been 

 observed in the sciatic nerve of frog, 

 record obtained with the optical 

 nerve is given later (fig. 404). 



I also give in the next figure 

 (fig. 325) a series of effects of 

 transmitted stimulation, which 

 show in a very interesting manner 

 the effect of fatigue in the modi- 

 fication of the conductivity of a 

 nerve. It is customary to suppose 

 that the nerve is indefatigable. 

 But I shall be able to show that 

 not only is the conductivity of a 

 nerve liable to fatigue, but its 

 excitability also. The demon- 

 stration of the latter will be given 

 in a succeeding chapter. For the demonstration of the 

 effect of fatigue on conductivity I selected a length of 

 10 cm. from the sciatic nerve of gecko. This was attached 

 for experiment to the Kunchangraph, in the manner 

 diagrammatically represented in fig. 315. The length B c, 

 which showed contraction, in response to stimulus trans- 

 mitted from A, measured 5 cm. The two exciting elec- 

 trodes, A a, were 2 cm. apart. The intervening tract, 

 through which excitation was transmitted, was, therefore, 

 3 cm. At" the beginning of the experiment, owing to the 

 depression of tone which the nerve had undergone, from 



M M 



FIG. 324. Record of Mechanical 

 Responses to Electrical Stimu- 

 lus obtained on Smoked Glass, 

 and given by the Optic Nerve 

 of Fish Ophiocephahis 



Note the abnormal positive re- 

 sponses passing through di- 

 phasic into normal negative. 



