SPECIES IDENTITY OF NUCLEUS-PLASMA NORM 461 



parison. When the factor of function is reckoned with, it is 

 probable that the nerve cell is not the exception it appeared to 

 be to Conklin's conclusion that within the same species cell 

 size is approximately constant. 



Since the data are meager, they were also examined mathe- 

 matically to see if there was anywhere a definite ratio of cell size 

 to body size with a progressive increase of body size. Experi- 

 ment Normal 18 (first and fourth series in table 5) was included. 

 By comparison of the ratio of body weight to body weight and 

 of cell size to cell size between Experiment ^Muscular Exertion 

 32 and Experiments Normal 18 and Normal 19 respectively, the 

 coefficient factors for body size are 2.4 and for cell size 1.8 in 

 the one (1 : 2.4 = 1.27 : 2.29) and 1.93 and 1.31 in the other 

 (1 : 1.93 = 1.27 : 1.67), which gives a disproportionately larger 

 size of cell in the smaller animal. Between Experimejits Cere- 

 bellar Section 4 and Normal 19, the coefficient factors are 

 1.45 and 1.48 (2.2 : 3.2 = 2.05 : 3.05), in which the cells main- 

 tain practically the same ratio as the body weight. Between 

 Normal 18 and Normal 19, the coefl^cient factors are 1.25 and 

 1.36 (2.57 : 3.2 = 2.24 : 3.05), which is in slight degree the 

 reverse of the first result, 



A priori, I feel as certain as one can that no exact correspond- 

 ence of nerve cell size to body size will be found. The unpub- 

 lished study of the development of function has molded the opinion 

 that it is the factor of individual function in the nerve cell which 

 fundamentally determines the size of its resting cell and nucleus. 

 Its principal growth is functional growth. Primarily, size will 

 vary according to function. On this basis, the striking exception 

 to any correspondence exhibited by the Purkinje cells of Experi- 

 ment Muscular Exertion 31 is readily explained. Some further 

 discussion is connected with the section on "Significance of the 

 constant nucleus-plasma relation." 



It must be distinctly understood that this lack of corre- 

 spondence does not distm'b the fixity of the relation between 

 the plasma and the nucleus. Whatever the absolute size of the 

 cell, that is constant. Certain points will emphasize how varia- 

 tions in one element of the cell are always complemented in the 



