669 
It has appeared in the first place that the volume of homologous, 
at the same time analogous ganglion cells (functioning in the same 
way) varies proportional as the power 0,27 or 5/;s of the body weight. 
As it further appears from the found equality of the relations of 
different kinds of neurones and the brain, that the same mechanism 
must hold for all the neurones, we can study it by means of the 
neurones with peripheral nerve fibers, which are most accessible to 
investigation. In animal species having the same form the length of 
homologous nerve fibers varies necessarily in direct ratio to the 
length of the body, ie. to P°33 or P's, in animal species of dissi- 
milar form the nerve lengths vary with a greater or smaller power of 
the body weight. In case of dissimilarity as well as in case of similarity 
in form the volumes of homologous, at the same time analogous neurones 
are however, found varying in proportion to P° or P%>. Hence 
the cross section of the nerve fiber must vary in inverse ratio to 
its length. As the nerve fiber constitutes by far the greater part of 
the volume of the neurone, the variation of the cross section may 
be put proportional as Pe? or P* for animal species having the 
same form, but different sizes. 
Man and the Mouse are not species of similar form; the Mouse 
has relatively much shorter limbs, nevertheless homologous neurones 
which function in the same way, such as the motor neurones for 
the finger muscles, can very well be compared, which appears from 
the careful measurements by Irvine Harpesty*). He found the nerve 
fiber of these neurones on an average 35 mm. long in full-grown 
mice, and the homologous nerve fiber of a man weighing 72 kg., 
i.e. 3600 times the weight of the mouse, 800 mm. long. These 
lengths are to each other as 22.86:1, i.e. as the power 0.3821 of 
the body weights, whereas in case of conformity the proportion 
would be as the power 0.33 of the body weights or 15.32: 1. The 
length of the nerve fiber of man ought then to be no more than 
536 mm. From Harpesty’s measurements of the diameters of the 
axones, the nerve fiber of man appears, however, to be thinner in 
exactly the same ratio as it is longer. The area of the cross section 
varies proportionally as the power 0.1693 of the body weight, 
instead of as the power 0.22 in case of similarity. Thus it is found 
that the volumes of these dissimilar neurones are exactly in the 
ratio of the power 0.55 or %/ of the body weights, and the square 
') Ixving Hanpesty, Observations on the Medulla Spinalis of the Elephant with 
some Comparative Studies of the Intumescentia Cervicalis and the Neurones of the 
Columna Anterior. Journal of Comparative Neurology, Vol. XII 1902, p. 171—172. 
