726 



sions, although the rate of the locomotion is equal. For this, 

 increase of the accumulated influxion in the cell-body of the neurone 

 is required, and hence of its volume, in the ratio of about ^^P or 

 po.33. Ij, about the same ratio the lengths of the nerve fibers of 

 homoueuric animal species necessarily increase, these lengths being 

 nearly proportionate to the longitudinal dimensions of the animals. 

 At the same time, it may l)e assumed, as a matter of course, that 

 there is a tendency for the homologous nerve fiber to increase with 

 the least possible defoi-mation. Witliout any deformation its area of 

 section should increase in the ratio of 7^*^ --•, while its length increases 

 in the ratio of po-33 . 



On the other hand, the mode of propagation of nervous influxions 

 being similar in homoueuric species of animals, the oidy possibility 

 to obtain this similarity, i.e. physiological homoneury, under the 

 given conditions, is that the area of section of the nerve fiber should 

 increase proportionally nnth its length. Therefore the area of the section 

 of the fiber has become somewhat greater and its length less than 

 for uniformity of the homologous nerve fibers, both in the ratio 

 of poo55.. Hence the ratio P^'^'"^ ■■'. 1, as was discussed in the outset. 



p 0.211 . —- po.Sn-^. . /J0.055. _- /.>0.222 . \^ p 0.055 . -_ p 0.211 . 



Thus the accumulated influxion, the time and the I'ate of propagation 

 increase, as they ought to do, in the same ratio. 



Through this way of viewing the matter, which starts from the 

 relations of quantity existing in the nervous system, many impon- 

 derabilia, such as the mental height, the intelligence, and not seldom 

 also the degree of brain evolution may be eliminated from the 

 foreground of our considerations of the relation between structure 

 and functions of the nervous system, which can only promote the 

 fruitfulness of researches in this region, among others and particu- 

 larly with regard to the cortex of the brain. 



A striking proof for this is furnished by Otto Mayer's researches 

 on the density in which the cells occur in the cortex of the brain 

 of Apes'). He namely determined, for seven genera, the mean 

 number bf cells per O.OJ cubic millimeter, in 10 fields (according to 

 Brodmann), throughout the whole thickness of the cortex. His results 

 induced him to point out emphatically that the densities by no 

 means run parallel with the order of the examined animals in the 

 zoological system, their degree of brain organization or their intel- 



1) Otto Mayer, Mikrometrische Untersuchungen über die Zelldichtigkeil der 

 Grosshirnrinde bei den AfTen. Journal fur Psychologie und Neurologic. Band 19. 

 Leipzig 1912, p. ^233—251. 2 Tafeln. 



