671 
How can we account for this constant deviation from the simple 
proportion between the cell-volume and the length of the body? 
We are put on the right track of this explanation by a dissimi- 
larity of the cell in relation to its nerve fiber. We found that in 
similar animal species of different sizes, the area of the cross section 
of the nerve fiber varies in proportion to Po22 or Ps With uni- 
formity of the ganglion cell from which the nerve fiber proceeds, 
this section would have to vary with the °/3 power of the volume 
of this cell, so that the cell volume itself would then have to vary 
proportionally to P°3 or P's, In reality the cell volume increases 
and decreases proportionally to Ps Whence this unconformity in 
animal species of similar form ? 
The answer to this question is supplied by the closer examination 
of the cell volume. Only part of it, the plasm, is in direct relation 
to the nerve fiber; the axis cylinder arises in the plasm, its structure 
proceeds in it, passing by the nucleus. 
It has already been known for some time, especially with regard 
to the large ganglion cells, that the size of the cell increases more 
than the size of the nucleus, hence the cytoplasm still more so *). 
The existence of a definite quantitative relation can here again be 
found by means of a power-equation. When the volumes of a large 
and a small cell C and C,, and those of the nuclei A and K, are 
known, the value of the power & for the relation between the two 
relative volumes can be calculated by means of the equation: 
In table I I have collected the diameters of a number of nerve 
cells and their nuclei, borrowed from the works of GauswePr Levi 
(1906 and 1908)'). Of course only between cells having the same 
Bd. 119 (1907), p. 574) gives 5.14 micra for the diameter in the Hare, and 4.6 
micra for that in the Rabbit. The relative cross section 1.248 is here proportional 
to the °/;, power of the relalive body weight. 
') Giuseppe Levi, Studi sulla grandezza delle cellule. I. Ricerche comparative 
sulla grandezza delle cellule dei Mammiferi. Archivio [taliano di Anatomia e di 
Embriologia. Vol. V. Firenze 1906, p. 291—358. Cf. on the relation of nucleus 
and plasm of the ganglion cells, the tables and graphic figures, particularly the 
table of the spinal ganglion cells, p. 330, and the two figures XIX, and also the 
conclusions formulated p. 354. 
Further data in: G. Levi, | gangli cerebrospinali. Studi di Istologia comparata 
e di Istogenesi. Supplemento al Vol. VII dell’ Archivio Italiano di Anatomia e di 
Embriologia. Firenze 1908. 392 pp., 60 Tavole. (These papers will be referred to 
as 1906 and 1908). 
