Every such muscular contraction as we have just described is brought about by means of a nervous impulse, originating at a receptor organ, either external or internal, which impulse proceeds toward a muscle or a group of muscles. However, this impulse (which in a sense may be thought of as a desire on its way to fulfilment), is often subject to a rather eventful history of interruptions before it finally produces muscular action. Between the individual nervous strands along the pathway of its motion the impulse may encounter blockades, unless electrically charged particles (called _ions_) are present at the various gaps in considerable numbers. Here again, then, we reach a further refinement in our understanding of what one class of “good” means. The “permeability of the synapses” (to use a phrase descriptive of the above situation), thus becomes a large determinant in human action. And if one of the classes of our concept is definable in terms of actions that are facilitated, the light which neurology throws upon ethics is not to be despised. Our next adventure is the search for the various implications of the term “good” as employed with respect to Class B. This class, as previously stated, involves the general notion of _dependability_. Things of this class are nominally useful, fit, or serviceable, not merely with reference to the desire of the moment, but also and more particularly they are useful for the future also. Nevertheless, this phrase, “useful for the future,” must be taken to mean “imagined as continuously or continually useful,” for although we commonly regard tomorrow as a sort of package that is coming to us in the mail, it is strictly something not yet existing and consequently unreal. Just as William James said, “The feeling of past time is a present feeling,” so is the feeling of dependability here to be interpreted not as a property of objects, but as a condition of the organism. And, while no incontrovertible evidence of the nature of such a condition has yet been brought to light, it is directly in line with the facts as we know them to assert that the “good” included in Class B implies both a maintenance of muscular tone and a steady permeability of the synaptic membranes involved in the action-patterns aroused by the things we keep calling “good.” To which we might also safely add, that the receptor organ requisite for initiating such an energy transformation has also become so attuned to receiving the stimulus as to show what the psychologists call a lowered threshold. Suppose we now condense this whole account, and state it more pointedly by saying that Class B refers to those objects that produce the responses for which the organism has mobilized its maximum available energies. Some of these dependable “goods” may thus imply habitual responses, while others may simply imply a craving long denied its overt satisfaction. And I doubt not that between these two extremes every man can find his own “highest _good_.”