448 DAVID H. DOLLEY 



well among different individuals as to have the exactitude of 

 truth. 



Accordingly, for the sake in part of supplying for the dog this 

 deficiency of data, the present series of measurements was under- 

 taken. Another and more immediate reason was that in a study 

 of the development of function in the dog which has recently 

 been carried on by Mr. Albert L. Jones and myself, the progress 

 of the nucleus-plasma relation from the embryonic condition 

 to that characteristic of full development has been consistently 

 in harmony with a law of constant correspondence of size re- 

 lation for the resting mature Purkinje cell. Consequently, it 

 seemed advisable to make additional measurements from a wide 

 assortment of animals, in order, if it continued to work out in 

 harmony, to make the induction more sure and as well to elimi- 

 nate reasonably the possibility of variations due to differences 

 in age, size, breed, or accidental causes other than those which 

 a priori should affect the constancy of the relation. 



The species identity will be shown to hold for the resting 

 Purkinje cell of the dog as well as for all resting cells of Cambarus 

 virilis. The mechanism of function in both is identical ('13 a), 

 the reaction of function is a purely quantitative one ('13 b), 

 and the cell recovers to its prior state of constancy after function 

 ('11 a). The actual figures from measurements of the stages 

 of activity have corresponded so closely among different indi- 

 viduals as to lead naturally to the induction that members of 

 a species must be to a remarkable degree on the same plane as 

 concerns the quantitative relation of nucleus to plasma. There 

 was therefore considerable collateral evidence pointing to a law 

 of species identity, from the study of functional activity origi- 

 nally and of the development of function later, before the facts 

 to be presented were sought. As a matter of logic, therefore, 

 the present induction of a law is not based on a relatively few 

 cases of coincidence, but the ground could be defended that 

 these cases represent a verification, the final step in inductive 

 logic. 



The evidence again from all sources indicates that there is 

 the same unity of mechanism for all other nerve cells (ill b); 



