Hardestv, Medulla Spi)ialis of the Elephant.- 173 



the area of the substantia grisea contained in the section of the 

 elephant is 54 times that of the mouse and its body weight 

 180,000 times greater. 



Comparing man with the mouse, man has a neurone whose 

 entire volume is 90 times greater than that of the mouse ; a 

 cell-body whose volume is 13 times greater ; the mean diameter 

 of the cell body, 2 times greater ; a section of medulla spinalis 

 with an area 47 times that of the mouse ; an area of substantia 

 grisea in section 15 times as great, and a body weight 3628 

 times as great. 



The above comparisons indicate that in a series of mam- 

 mals of varying body weights, the volume of the entire neurone 

 varies more nearly in proportion to the variations in body 

 weight than either the area of the section of the medulla spin- 

 alis, the area of the substantia grisea contained in the section, 

 or either the diameter or volume of the cell-body contained in the 

 substantia grisea. 



The other members of the series would show slightly dif- 

 ferent and equally interesting relationships but it would be too 

 tedious to continue these comparisons further. The elephant, 

 man and mouse are chosen because they represent species hav- 

 ing fairly uniform size, because they are forms of which we 

 have a more definite impression, and because at the same time 

 they represent the extremes and the mean of the series. 



From the measurements cited and those recorded in Table 

 III, and from the above deduced comparisons, it may be 

 advanced : 



1. That the size of the large cell bodies situated in the col- 

 umnae anteriores as well as that of the cell-bodies in the ganglia 

 spinalia varies appreciably in adult mammals of different sizes. 



2. That in general the larger mammals have the larger 

 cell-bodies in both localities, but that in either the variations in 

 the size of these cell-bodies do not occur in the same ratios as 

 the variations in the size of the body of the animals, the cell 

 bodies varying in much smaller ratios than the body weights. 



3. That the variations in the volumes of the cell bodies 

 do not occur in higher ratios than the variations in the areas of 



