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 

 1799.'' 



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. 



