METHODS OF PHYSIOLOGICAL RESEARCH 33 



Here, according to du Bois-Reymond, we stand at one limit of our 

 knowledge of nature. 



What an atom is, i.e., what matter endowed with energy is, the 

 world-formula does not explain. If we ask how we arrive at the 

 conception of an atom, we find that we conceive it as an exces- 

 sively small, indivisible, elementary part of a body, derived by con- 

 tinued division of the body ; but if a body be continually divided 

 until its atoms are reached, nothing but body is obtained. Atoms 

 are bodies, and have the general characteristics of bodies. We 

 cannot, therefore, expect to obtain by division something that 

 elucidates the nature of the body. When we explain an unknown 

 phenomenon by the motions of atoms, we merely resolve it into 

 unknown phenomena. What an atom is, we do not learn, for it 

 has only the properties which we attribute to it on the basis of the 

 sense-perception of what large bodies show us, i.e., it is hard, im- 

 penetrable, possesses form, and moves. But we obtain not the 

 slightest information regarding the nature of the matter that is 

 endowed with energy, i.e., that of which the physical world con- 

 sists. Our craving for causality remains, therefore, in this respect 

 unsatisfied, and as the result of our analysis we find ourselves at 

 the first limit of our knowledge. 



But this is not the only limit. If, again, we possessed " astro- 

 nomical knowledge " of the physical world, as du Bois-Reymond 

 expresses it, i.e., the same mathematically exact knowledge of the 

 motions of atoms that we have of the motions of the heavenly 

 bodies, we would then, indeed, understand all phenomena of the 

 physical world, but we would not understand how consciousness 

 arises, how in general a psychical phenomenon, even the very 

 simplest, comes to be. If we had, e.g., astronomical knowledge 

 of our brain, we would know the position and motion of every 

 atom at every moment ; we could also follow definitely the specific 

 physical changes, rearrangements, and motions of atoms insepar- 

 ably associated with specific psychical phenomena, and " it would 

 be," as du Bois-Reymond says, " of unbounded interest, if with our 

 mental eye turned inward we could observe the cerebral mechanics 

 of an arithmetical problem, like the mechanics of a calculating 

 machine ; or if we could know what dance of the atoms of carbon, 

 hydrogen, nitrogen, oxygen, phosphorus and other elements, cor- 

 responds to the delight of musical sensation, what whirl of such 

 atoms to the acme of sense-enjoyment, what molecular storm to 

 the frantic pain resulting from maltreatment of the nervus 

 trigeminus." 



We could know all these if we possessed " astronomical know- 

 ledge " of the brain. We could thus convince ourselves by self- 

 observation that consciousness is inseparably associated with 

 atomic motion. But with all this it would remain for ever con- 

 cealed from us how consciousness arises, how the simplest psychical 



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