CONCLUSIONS AND SUGGESTIONS 173 



ness cannot exist unless transportation is uniform and 

 constant in rate in all parts at each level and the sub- 

 stance is gradually destroyed or transformed during 

 the transportation. The dynamic theory affords an 

 adequate basis for the very definite range of dominance 

 which we find in organisms, and a chemical theory 

 does not. 



Tashiro's recent investigations on carbon-dioxide 

 production and my observations on susceptibility 

 gradients in the nerve indicate that physiological domi- 

 nance in the neuron, i.e., the direction of transmission, is 

 associated with the existence of a metabolic gradient. 

 Individuation in what is probably the most highly 

 specialized cell individual in the organism apparently 

 starts from the same condition, the metabolic gradient, 

 as in the simplest axiate animal or plant. It is certain 

 that dominance in the neuron depends primarily on 

 transmission and not on transportation. This argu- 

 ment from the highly specialized to the simple is 

 perhaps not of great value; still I cannot but believe 

 that the existence of an axial gradient in metabolic 

 rate in the neuron and in the simple axiate individuals 

 among the lower organisms is a fact of real significance. 



It has been very generally believed by physiologists 

 that the nerve, at least the medullated nerve of verte- 

 brates, transmits excitations under normal conditions 

 without a decrement in energy or intensity. It is, 

 however, a well-known fact that even in these nerves a 

 decrement appears when transmission takes place at 

 low temperature or in partially narcotized or com- 

 pressed nerves; in fact, under various conditions which 

 decrease metabolic rate or irritability in the nerve. 



