62 ON MAGNITUDE [ch. 



dimensions, and therefore about eight times greater in volume or 

 in mass. But making due allowance for difference of shape, the 

 linear dimensions of the elephant are to those of the mouse as not 

 less than one to fifty ; and the bulk of the larger animal is something 

 like 125,000 times that of the less. It follows, if the size of the 

 nerve-cells are as eight to one, that, in corresponding parts of the 

 nervous system, there are more than 15,000 times as many individual 

 cells in one animal as in the other. In short we may (with Enriques) 

 lay it down as a general law that among animals, large or small, the 

 gangUon-cells vary in size within narrow limits; and that, amidst 

 all the great variety of structure observed in the nervous system 

 of different classes of animals, it is always found that the smaller 

 species have simpler gangha than the larger, that is to say ganglia 

 containing a smaller number of cellular elements*. The bepiing of 

 such facts as this upon the cell-theory in general is not to be dis- 

 regarded; and the warning is especially clear against exaggerated 

 attempts to correlate physiological processes with the visible 

 mechanism of associated cells, rather than with the system of 

 energies, or the field of force, which is associated with them. For 

 the life of the body is more than the swm of the properties of the 

 cells of which it is composed: as Goethe said, "Das Lebendige ist 

 zwar in Elemente zerlegt,* aber man kann es aus diesen nicht wieder 

 zusammenstellen und beleben." 



Among certain microscopic organisms such as the Rotifera (which 

 have the least average size and the narrowest range of size of all 

 the Metazoa), we are still more palpably struck by the small number 

 of cells which go to constitute a usually complex organ, such as 

 kidney, stomach or ovary ; we can sometimes number them in a few 



* While the difference in cell-volume is vastly less than that between the 

 volumes, and very much less also than that between the surfaces, of the respective 

 animals, yet there is a certain difference ; and this it has been attempted to correlate 

 with the need for each cell in the many-celled ganglion of the larger animal to 

 possess a more complex "exchange-system" of branches, for intercommunication 

 with its more numerous neighbours. Another explanation is based on the fact 

 that, while such cells as continue to divide throughout life tend to uniformity of 

 size in all mammals, those which do not do so, and in particular the ganglion cells, 

 continue to grow, and their size becomes, therefore, a function of the duration of 

 life. Cf. G. Levi, Studii sulla grandezza delle cellule. Arch. Jtal. di Anat. e di 

 Embrioloq. v, p. 291, 1906; cf. also A. Berezowski, Studien liber die Zellgrosse, 

 Arch. f. Zellforsch. v, pp. 375-384, 1910. 



