Weiss's and Hoorweg's laws are discussed with respect to the dynamics of the excitatory process. The former is shown to have a simple basis which is inadequate, however, because it implies a constant rate of subsidence of the state of excitation. Hoorweg's law does not follow logically from the same basis so the two laws do not represent the same excitatory mechanism. Experimental data do not give minimal energies at 2 rheobases as predicted by each law. The experimental minima with direct currents are at 1.5 or more rheobases, while with condenser stimuli they are from 2.5 to 3.0 rheobases. These minima conform to the predictions of the writer's equations which give the direct current minima as variable with a lower limit at 1.5 rheobases and the condenser minima as constant at e = 2.718 rheobases. The reasons for these differences are discussed and it is concluded that considerations of the quantity of electricity and the energy, per se, do not lead to any simple concepts with regard to the excitatory mechanism. The existing quantity and energy relations are, however, easily correlated in terms of the dynamics of the excitatory mechanism.