THE NATURE OF STIMULATION 21 



unknown factor instead of being content with the simple descrip- 

 tion of facts, such as Kirchhoff^ has advanced in the field of 

 mechanics. Although of late natural science has also dispensed 

 more and more with conception of force as a means of explana- 

 tion, it is still today not wholly done away with. That which 

 applies to the conception of force is likewise true of the concep- 

 tion of cause. 



Another point concerning the application of the conception of 

 cause seems to me, however, to be of much more importance, 

 namely that a single cause is held responsible for the taking 

 place of a process. One endeavors to explain a process in gen- 

 eral by seeking for its "cause." The cause being found, the 

 process is considered as fully accounted for. This idea is not 

 only widely spread in everyday life, but is even found frequently 

 in natural science, especially in biology, although here, it should 

 be known, the processes are decidedly more complicated. The 

 search for the "cause" of development, for the "cause" of hered- 

 ity, for the "cause" of death, for the "cause" of the respiration, 

 for the "cause" of the heart beat, for the "cause" of sleep, for 

 the "cause" of disease, etc., was for a long time and frequently 

 even today a characteristic of biological investigation. As if 

 such a complicated process as development, death or disease 

 could be explained by a single factor! In reality, one has 

 obtained very little as a result of the analysis of a process by 

 discovering its cause ; and in addition the false impression arises 

 that through the finding of this one factor the process has been 

 definitely explained. It has been generally recognized in the 

 natural sciences in recent times that no process in the world 

 is dependent upon one single factor and attempts have been made 

 to give this fact more consideration. 



It is the custom at the present time to hold the view that every 

 process or state is brought about by its cause, but that a series of 

 conditions are also necessary to the production of the process. 

 Such a view, however, which considers that two different factors 

 existing at the same time are necessary to the accomplishment of 



1 Gustav Kirchhoff : "Vorlesungen uber mathematische Physik. Mechanik." Leipzig 

 1876. 



