INDIVID UATION AND REPRODUCTION 219 



within a shorter distance than in the normal nerve. It is impos- 

 sible to consider the literature of this much-discussed problem here, 

 but it may be said that there is considerable evidence which indi- 

 cates that a decrease in energy or effectiveness occurs in the course 

 of transmission, even in the most highly developed nerve fibers, 

 while, up to the present time, no one has actually demonstrated 

 that conduction without decrement over any considerable distance 

 occurs. It appears, then, that transmitted excitations in organisms 

 do in general show a more or less rapid decrement and conse- 

 quently a limit of effectiveness at a greater or less distance from the 

 point of origin. In other words, such excitations gradually die 

 out like a wave or an electric impulse, but the more intense the 

 excitations or the better the conducting path, the greater the dis- 

 tance between point of origin and limit of effectiveness. From our 

 knowledge of conduction of excitations in non-living substances, 

 this is what we should expect in conduction in living substance. 



If the dominance of one region over another in the organism 

 depends upon such transmitted excitations, there must be a spatial 

 limit to such dominance. And since the excitations which proceed 

 from the dominant region must result from metabolic changes 

 occurring there, we should expect to find them varying in intensity 

 with the rate of metabolism in the dominant part. Moreover, the 

 more intense the excitation and the better the conductor through 

 which the excitation is transmitted, the greater its effective range, 

 i.e., the distance to which it can travel before becoming ineffective. 

 Consequently the spatial limit of dominance must vary with the 

 rate of metabolism in the dominant part and the efficiency of the 

 conducting path between that and other parts. In the plants and 

 lower animals and in early stages of embryonic development of all 

 forms the efficiency of conduction is low and dominance is in general 

 effective over rather limited distances. In the later stages of 

 development of those forms which possess a nervous system the 

 efficiency of conduction increases very greatly as the nerves 

 develop, and the spatial limit of dominance likewise increases very 

 greatly. 



In the plants and lower animals the limit of dominance is indi- 

 cated very clearly by the size of the individual or part concerned, 



