1336 



IVie volume of the neurone increases proportionally to the square 

 of the increasing volume of its central part, the cell-body. 



Thus we come to the conception that the tnhole of the brain- 

 volume, inclusive of all that we are used to consider as intermediate 

 and supporting substance (interstitium) of the effective elements, parti- 

 cularly also the neuroglia, forms just as well an essential entity as 

 the neurone with the medullary sheath : the brain is entirely built 

 up of neurones or of such elements, either cellular or non-cellular, 

 that physiologically belong to them, though known by different 

 names, as those connecting the spinal cord with the periphery of the body. 



The explanation of the fact that with increasing size of the body 

 the quantity of the substantia alba, which chiefly consists of nerve 

 fibers, increases to a disproportionally greater degree, in the spinal 

 cord and the brain, than the substantia grisea, which contains by 

 far the most cell-bodies, is an unsought result of the found propor- 

 tionality. This explanation is not in conflict with the imperative 

 nature of the neurone as cell, as other explanations were. 



On individual enlargement of the body within a species, the quantity 

 of the brain increases only in the ratio of S*^— or not much moi'e, 

 probably because the number of cell-elements does not increase here 

 in ratio of S^-'^'^ or somewhat less, i. e. of the length dimension of 

 the body, as it does for the increase of the size of the body from 

 species to species. It is self-evident that thus the mutual ratio of 

 the substantia alba and the substantia grisea in the central nerve 

 apparatus does not become different from that with bodily enlargement 

 of species, because every neurone behaves exactly the same in the 

 one case as in the other. 



The explanation of the factor S^"^^ , according to which the 

 neurone centre, the cell-body, increases in proportion to the body 

 weight S, is now to be found in the very particular behaviour of 

 the size of the eye. Large animals have relatively small eyes in com- 

 parison to their body weight; here exists a relation of a similar 

 nature as with regard to the quantity of the brain, which is likewise 

 relatively small for animals of high body weight. 



Shinkishi Hatai, Number and Size of the Spinal Ganglion Cells and Dorsal Root 

 Fibers in the While Rat at DifTerent Ages. Journal of Gomp. Neurology. Vol. 12 

 (1902), p. 121. Of twenry of the laigest cells in the sixth ganglion spinale and 

 twenty of the thickest nerve fibers in it of a white rat of a body weight of 167 

 grammes, for which maturity had been reached as regards size of the cells, the 

 mean diameters were resp. 52.7 and 13.9 micra. I found 78 mm. for the length 

 of the longest nerve fiber of the rat of this body weight. 



