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attached to that intermediate substance of the essential elementary 
components of the brain as to the coverings of the neuraxone. That 
these could not be entirely inactive, had been understood long ago. 
Just as the propagation of the process of stimulation in the axone 
has nothing in common with the conduction of the electrie current 
through a wire, the comparison of the medullary sheath to the 
insulator of an electric cable undoubtedly represents this living sub- 
stance as being much more passive than it is in reality, though it 
is true that it does not directly take part in the propagation of the 
impulses. Nor could the simple function of giving support and pro- 
tection to the neurones be assigned with conviction to the neuroglia. 
No more does the equality of the volume of the medullary sheath 
with that of the axone, which Donatpson and Hokn') established 
for all classes of Vertebrates, fit in with the view that the former 
would only have the same significance as the insulating covering 
of the conductor in the cable. 
Taking this into consideration and in view of what physiological 
experiments have taught, the nervous system, hence the neurone, 
appears more and more in the light of a mechanism; though a 
stringent proof could not yet be furnished, chiefly because it is 
only in the last few years that a relation has been found between 
dimension and function of the nervous system. Thus doubt could 
still be entertained, chiefly as regards the organ of the brain, of the 
rational significance of the determined quantitative relations, which 
beyond any doubt point to the existence of a (as yet unknown) 
mechanical relation. 
For — thus the reasoning ran — part of the brain must as “the 
organ of the mind” be as independent of the size of the body as 
the psychical processes that are enacted there; is it then possible to 
assume that the body mechanically determines the total quantity of 
the brain? ; 
But the psychical processes, certainly, are not independent of the 
quantity of the brain and its parts. For Man is not only psychically 
superior to all the animals, he is also distinguished by the great- 
est true relative brain quantity, and by the extraordinary develop- 
ment, particularly of that part of the brain which performs the 
highest functions. We also meet with great differences in the well- 
calculated relative brain quantity (determined by the cephalisation 
1) H. H. Donatpson and G. H. Hoke, On the Areas of the Axis Cylinder and 
Medullary Sheath as seen in Cross Sections of the Spinal Nerves of Vertebrates. 
Journal of Comparative Neurology and Psychology. Vol. XV. Chicago 1905, p. 1—16. 
