THE DEEPENING OF PHYSIOLOGY. 303 



of the obscure problems not only of nervous disease, 

 but of nervous life, by an analysis which is a tracking 

 out the devious and linked paths of nervous threads. 

 The very beginning of this analysis was unknown in 



We have noticed that in 1811, Charles Bell (1774- 

 1842) announced his "new idea" that the posterior 

 or dorsal roots of the spinal nerves are sensory in 

 function (conducting impulses centripetally ) , while 

 the anterior or ventral roots are motor in function 

 (conducting impulses centrifugally), a conclusion 

 afterwards proved, experimentally by Johannes 

 Miiller. 



The next great step was due to Johannes Miiller 

 (1801-1858), and was expressed in his doctrine of 

 the specific energies of the nerves and sense-organs 

 (1826). Different kinds of stimuli applied to the 

 same sense-organ always evoke the same kind of 

 sensation; or, conversely, one and the same stimulus 

 or the same external phenomenon, evokes different 

 sensations by acting on different organs. As Bunge 

 says : * " The phenomena of the outer world, 

 therefore, have nothing in common with the sensa- 

 tions and ideas they call forth in us, and the states 

 and processes of our own consciousness are alone im- 

 mediately subject to our observation and recogni- 

 tion." 



Miiller was right in his conclusion that, however 

 a particular nerve is stimulated, the message is 

 always of the same kind as that which is normally 

 delivered by the nerve; an unusual stimulus to the 

 optic nerve will result in visual sensation. But he 

 was wrong in ascribing the specific effects to the 



* Physiological and Pathological Chemistry. Trans. 1890, 

 p. 12. 



