METHODS OF PHYSIOLOGICAL RESEARCH 31 



female." But, if we despair of a chemico-physical explanation 

 of vital phenomena, nothing remains but to take refuge again in 

 the long-buried doctrine of vital force. In fact, very recently this 

 idea has again appeared in various places, notably in the writings 

 of Hanstein, Kerner, Bunge, Rindfleisch, and other men of 

 science. 



We might, however, be much more inclined to despair if we 

 should look at the field of psychical phenomena. In the physiology 

 of the brain and the sense-organs, indeed, much has been cleared 

 up concerning the physical relations of certain psychical processes. 

 But the old riddle of the causal relations between body and 

 mind, which occupied so fully the thinking intellect even in earliest 

 times, remains apparently wholly untouched by natural science. 



Under such disheartening conditions the investigator is constantly 

 oppressed by the questions : Are there limits to our knowledge of 

 vital phenomena ? If so, where do these limits lie ? Or are we 

 upon a false path ? Was our attitude of inquiry into nature a 

 mistaken one, so that we have not understood her answer ? 



B. THE RELATION OF PSYCHOLOGY TO PHYSIOLOGY 

 1. The Question of the Limits of a Knowledge of Nature 



Are there limits to our knowledge of nature ? And if so, where 

 do they lie ? These questions have repeatedly arisen in the present 

 generation, which is proud of its achievements in natural science, 

 and have been treated in various ways. We can most fittingly 

 consider them in connection with the well-known address of E. 

 du Bois-Reymond ('84), " Ueber die Grenzen des NaturerJcennens," 

 in which the recently deceased author, who was a master of lan- 

 guage among German naturalists, discussed this theme in his 

 accomplished style. 



With the lack of philosophical methods of thought which un- 

 fortunately is so wide-spread in the science of to-day, the most re- 

 markable ideas upon the basis of our knowledge of nature are 

 often met with. This circumstance unfortunately justifies specula- 

 tive philosophy in looking with contempt upon science, its rival 

 in the recognition of truth. It is, therefore, necessary to examine 

 these questions somewhat carefully, and, first, to inquire concerning 

 the limits of knowledge, not only in organic, but in all nature. 



Modern science, especially physics and chemistry, is here the 

 leader, and endeavours to reduce all the phenomena of the 

 physical world to motions of atoms. Accordingly, du Bois- 

 Reymond, in order to obtain a fixed point upon which to base 

 his considerations, defines a knowledge of nature as follows : " A 

 knowledge of nature more accurately expressed, scientific know- 



