1330 



about proportionately to the length of the animal, and the cell-bodies 

 in the central nerve apparatus, from which they start. 



Then we may ask: is it indeed a disproportion with which we 

 are occupied here? Will not the lengthening of the nerve liber 

 necessarily be accompanied by an increase of the volume of the 

 cell-body from which it arises, at least in a certain degree? The 

 starting point of the explanation indicated above and of other similar 

 explanations, given of the striking disproportion in the composition 

 of the brains, although admittedly equivalent, of two aminals different 

 in the size of their bodies, but equal in their organisation, would 

 then be wrong, and perhaps another explanation is to be found, 

 not leading to contradiction or even to absurdity. 



So the starting-point in (piestion, the supposed constancy of the 

 volume of the cell-body and the diameter of the nerve fiber certainly 

 calls for a closer enquiry. In the conception of the nei'vous system 

 as composed of specific cells, the neurones, it is of principal signi- 

 ficance to know what is the relation between the volume of these 

 cells, which are so particularly specialized, and between the volume 

 of their parts, and the body weight. 



For the longest and very peculiar process of the neurone, the 

 neurite or nerve fiber, it is unvoidable to assume that, when it 

 reaches the periphery of the body, its volume increases with the 

 length of the body, tliis implying an increase of the volume of the 

 neurone. Concerning the constancy or' variability of the volume of 

 its central |)art, the cell-botfy or "ganglion cell", in the s|)inal cord 

 or the brain, there still exists (unnecessarily) difference of opinion. 

 Many neurologists still (erroneously) consider the variations in the 

 dimensions as entirely accidental, and so slight that they are negligible 

 in our conceptions of the structure of the central nervous systeqn. 



There is, however, evidence that differences in the size of 

 homologous nerve cell-bodies constantly occur, in a certain relation to 

 the size of the body ; so that they have a real significance. 



These differences are most striking where we compare homologous 

 cells of animals, such as the elephant and the mouse, which differ 

 greatly 'in the size of the body. The largest central parts, "cell-bodies", 

 in the columnae anlerioies of the intumescentia cervicalis (6''' cervical 

 segment) of the Indian elephant have a diametei- above 3 times and 

 a volume more than 29 times that of the homologous cell-bodies 

 in the mouse. Apparently this is exceedingly little when compared 

 with ratios like that of the linear dimensions of the body (60:1) 

 and that of the body weight (180-000:1). Nevertheless a regular 

 proportion may exist, causing in the albino rat, the body weigth of 



