724 COMPARATIVE ELECTRO-PHYSIOLOGY 



begins to make its appearance. Up to this point, the nerve 

 as a whole has been undergoing increasing contraction, the 

 base-line of the series of records being thus tilted upwards. 

 But after D, it begins to show relaxation, and at the stage E, 

 the responses to individual stimuli are actually reversed, 

 the region of transformation from diminishing to reversed 

 response being often marked by the appearance of diphasic 

 (figs. 396 and 400). The entire responsive cycle may thus be 

 viewed as consisting of two halves of which one is the reverse 

 of the other. From the state of extreme sub-tonicity at A 

 with its abnormal positivity, the responses are transformed 

 through diphasic to feeble normal negative at B. They here 

 increase in a staircase manner, till they become uniform at C. 

 After this begins the reversing process, due to fatigue, 

 brought on by overstrain, with its diminishing normal re- 

 sponses at D, through diphasic, to abnormal positive once 

 more, at E. Excessive sub-tonicity and excessive stimulation 

 alike find their extreme case in the abolition of all response 

 at death. The difference between the abnormal positive 

 response of sub-tonicity and the abnormal positive response of 

 fatigue lies in their previous history. The one is due to lack 

 of stimulation and the other to its excess. For the restoration 

 of normal response, the treatment in the two cases must be 

 opposite. In the first, the application of stimulus is necessary ; 

 in the second, it is its cessation, or rest, which is required. 



Similar effects are also met with, in the case of trans- 

 mitted excitation. In the sub-tonic condition, conductivity 

 is depressed, and the transmitted effect is abnormal positive. 

 By the action of stimulus, however, the conductivity is 

 gradually restored, and the response to transmitted stimu- 

 lation is converted from abnormal positive to normal 

 negative through the intermediate diphasic. After this, 

 under increasing fatigue the diminishing responses are con- 

 verted to abnormal positive through an intermediate diphasic 

 (fig- 3 2 5)- Another important demonstration was that of the 

 perfect similarity of the molecular changes induced by 

 stimulus in the afferent and efferent nerves respectively. 



