THE WORLD OF LIVING ORGANISMS 147 



supported by many eminent men ; but the more the central 

 nervous system is investigated, the less are such hopes 

 realised. We might at least expect that the very marked 

 centralisation which is expressed in the apperceptive process 

 of our ego, should be discoverable in the central apparatus 

 of the body. 



Instead of which, the investigator finds nothing but a 

 guiding apparatus, which serves to connect the two " fronts " 

 of the body — the one, the receptor, turned towards the world- 

 as-sensed, and the other, the effector, towards the world of 

 action. 



In its main features, the guiding apparatus is the same 

 from the lowest animals to the highest. Wheresoever quali- 

 tatively different stimuli effect an entry, we find that their 

 specific peculiarity is taken from them. Whether an air- 

 wave strikes the ear, or an etheric wave the retina, the same 

 transformation is set going in both cases. A excitation is 

 around, which passes along the nerves in waves. The length 

 and speed of these waves may vary to a certain degree, but 

 fundamentally the process is always the same. The various 

 stimuli are not distinguished through different excitations in 

 the nervous system, but by the " person " of the nerves 

 through which they flow. We have already said something 

 about this fundamental law of the nervous system : it was 

 discovered by Johannes Miiller, who made of it, along with 

 all its corollaries, the basis of comparative physiology of the 

 nervous system. 



Nervous excitation itself is a process hitherto unexplained, 

 which reveals itself as electrical oscillatory waves on the 

 galvanometer, or as chemical waves of fibrillar staining. 



The idea we get of it in these ways does not suffice to 

 give us a general survey of the way in whicli excitation 

 operates in the system as a whole ; so the physiologist must 

 make use oi a current analogy, and treat the whole nervous 



