34 GENERAL PHYSIOLOGY 



phenomenon comes to be. However carefully we might follow the 

 motions of individual atoms in the brain, we would see only 

 motions, collisions, and again motion. Thus, it is evident that a 

 mechanical explanation of consciousness, of psychical phenomena, 

 from the motions of atoms is an impossibility for us, and we find 

 ourselves at a second limit of our knowledge of nature, which ap- 

 pears not less impassable than that of a knowledge of matter and 

 energy. 



But supposing the first to be passed, and the riddle of matter 

 and energy to be solved, how would it be with the second limit ? 

 Would it be passed at the same time or would it still be impass- 

 able ? We can evidently imagine consciousness, or rather the 

 simplest form of mind, to be inherent in the nature of an atom, 

 and, therefore, to be known when the nature of matter is known. 

 In fact, this idea would be the only one that could be adopted by a 

 monistic science, which seeks to explain all phenomena by one 

 principle ; and Haeckel especially, who is an energetic advocate of 

 monism among men of science, has always maintained it. du 

 Bois-Reymond alludes to such a possibility only briefly when he 

 says : " Finally, the question arises, whether the two limits of our 

 knowledge of nature may not perhaps be the same, i.e., whether, if 

 we understand the nature of matter and energy, we may not also 

 understand how under certain conditions matter may have sensa 

 tions, desires, and thoughts. This idea is, of course, the simplest 

 one, and according to the known principles of investigation is pre- 

 ferable to its opposite, according to which, as before said, the world 

 appears doubly inconceivable. But it lies in tfye nature of things 

 that we cannot elucidate this point, and all further words concern- 

 ing it are idle." Therefore, " as to the riddle of matter and energy 

 and their conceptions," du Bois-Reymond decides upon complete 

 renunciation and proclaims to science not only a temporary 

 " ignoramus," but an eternal and demonstrative " ignorabimus" 



2. Physical World and Mind 



We have followed du Bois-Reymond's course of thought thus in 

 detail, in order to show that the knowledge assumed by him as 

 the starting-point of his considerations very soon encounters 

 obstructions, in view of which the world appears incomprehensible. 

 But eternal renunciation falls heavily upon the indefatigable 

 thinker, and he is bound to ask whether this assumed path of 

 knowledge is a right one, whether the definition of a knowledge 

 of nature as a resolution into the mechanics of atoms is correct 

 or justified. We will, therefore, test this basis of our considerations 

 and inquire what knowledge is. 



For this purpose we will take the conception " knowledge " in 



