SPECIFIC ENERGIES OF NERVE-CELLS. 285 



is irrational, because in these processes it gives pro- 

 minence to an accidental circumstance, tliat is, to the 

 way in which they affect human beings, who are endowed 

 with various sensations, while in other, such as mag- 

 netic and electric processes, it is based on quite different 

 marks of classification. Scientific study of the phy- 

 sical processes on the one hand, and of the physio- 

 logical processes of sensation on the other, exposes this 

 error, which penetrates further owing to the fact that 

 language uses the same words for the different pro- 

 cesses, thus making their distinction harder. 



Language is, however, but the expression of the 

 human conception of things, and the conception of 

 the innate identity of light and the sensations of light, 

 of sound and of the sensation of sound, and so on, was 

 regarded till quite recently as incontrovertibly true. 

 Goethe ^ gave expression to this in the lines — 



War' nicht das Auge sonnenliaft, 

 Die Sonne konnt' es nie erblicken ; 

 Liig' nicht in was des Gottes eigne Kraft, 

 Wie konnt' uns Gottliches entziicken ! 



Plato expresses himself in the same way in the 

 ' Timaeus.' On the other hand, Aristotle held correct 

 conceptions on the subject. But it is only since the 

 researches of Johannes Miiller laid new ways open to 

 science that these conceptions have gained a scientific 

 foundation, and have been brought in all points into 

 harmony with the facts, so that they have now become 

 the basis of the physiology of the senses and the 

 psychology of the present day. 



One expression of the erroneous views once pre- 

 valent is to be found in the theory of so-called ade- 



' Zahne Xenien, iii. 70. 



