70 IRRITABILITY 



of rest, would, therefore, be metabolism of stimulation, but one 

 that is characterized by a constantly existing metaboHc equilib- 

 rium. 



This "equilibrium of metabolism" distinguishes the metabolism 

 of rest from that form which is developed in response to tem- 

 porary stimulation, in that every temporary stimulation has the 

 effect that it disturbs the existing metabolic equilibrium for a 

 longer or shorter time. This disturbance of the equilibrium of 

 metabolism can in contrast to the metabolism of rest be termed 

 "metabolism of stimulation." In this, but only in this sense, can 

 these two conceptions be placed in opposition and used to char- 

 acterize the processes in the living organism. The conception 

 of the metabolism of stimulation must always stand in relation 

 to that of an equilibrium of metabolism characterized by a con- 

 stantly existing metabolism of rest, just as the conception of 

 stimulus can likewise only be defined relatively to that of vital 

 conditions. 



Nevertheless, the conception of the equilibrium of metabolism 

 requires a somewhat more accurate definition before we can feel 

 justified in using this term. Definitions are always trite, never- 

 theless they are the basis of all our thinking and a definite under- 

 standing is impossible unless we first clearly fix their contents. 

 The history of theology and philosophy even to the most recent 

 times furnishes a long line of instances in which the most eminent 

 minds, for the want of fixed definitions of the conceptions which 

 they made use of, failed to find a mutual basis for their ideas. 

 Without a sharp definition every conception is a mere word, 

 which each individual, according to his personal experiences and 

 views, endows with a different meaning. To such conceptions 

 we may apply Mephisto's ironical comment to his pupil : 



" Mit Worten lasst sich trefflich streiten, 

 Mit Worten ein System bereiten." 



The natural sciences, if they are to retain their reputation for 

 exactness and precision, require the strictest and clearest defini- 

 tions of all conceptions. If we seek to penetrate more deeply 

 into the varied happenings in concrete conditions, we must recon- 



