Fatigue of Excitation and Fatigue of Depression etc. 47 



determine the exact single effect in the case of any stimulus or to 

 analyze its diverse effects (by proper adjustment of strength and time) 

 with the exactitude belonging to that method, a valuable supplement 

 to primary physiological study." It will only be said here that it 

 depends upon the fortunate fact that the degree of previous activity 

 and the depression which ensues to hold it at a standstill are inde- 

 pendently diagnosticable in the same cell. 



The Distinction between Fatigue of Excitation and Fatigue of 



Depression. 



So far as confusion exists as to the cause of the anatomical 

 changes of activity, as indicated in the introduction, it may be traced 

 to the neglect of the distinction expressed under this section heading. 

 Undoubtedly too much importance has been attached to the accumu- 

 lation of fatigue substances in speculating on the process and results 

 of functional activity. There is nothing new in the distinction, for 

 it was pointed out by Verworn nearly twenty years ago. To quote 

 for the statement of it from the translation of his General Physiology, 

 "Phenomena of fatigue are observed, on the one hand, when certain 

 substances that are necessary to life are consumed during exhaustive 

 activity more rapidly than they are introduced or reformed; and, on 

 the other, when certain substances that arise as decomposition pro- 

 ducts during activity accumulate in such quantity that they produce 

 a depressing effect." In short, there is one kind of depression due 

 to waste products and another due to the consumption within the 

 cell of substances necessary to life. 



It is not difficult to discern the explanation of the neglect of 

 the distinction in physiological studies of the nerve cell. This is that 

 the two different causes have one and the same ultimate effecl on 

 function, the external work. If carried to a maximum, both processes 

 lead to a complete cessation of function. In the one case, it is be- 

 cause function is blocked, in the other, it is because there is no more 

 material to work with, so that the stoppage may be absolute in either 

 case. Exhaustive activity then ends in depression. From this end re- 

 sult, a progressive depression from the beginning as regards function- 



