128 COMPARATIVE ELECTRO PHYSIOLOGY 



the normal reactions, however, under abnormal conditions, 

 they may be reversed. Thus, excessive cooling or strong 

 external stimulation may reverse the normal current of rest. 

 There are, moreover, two different conditions, those, namely, 

 of sub-tonicity (cf.p. 106) and fatigue, which may be effective 

 in bringing about a reversal of the normal direction of the 

 responsive current. In this way, by means of induced varia- 

 tions of the resting-current and of the responsive current, 

 many very varied effects become possible. 



