ABSTRACT
Anxiety is a common experience that one would be disinclined to believe anyone who claimed to be immune to it, but its precise nature and function are by no means self-evident. Anxiety of this kind is, in principle at least, a symptom, even though it may occur so infrequently and may appear so trivial that it would be absurd to suggest that everyone who has ever experienced it should seek psychiatric treatment. Anxious concern also resembles apprehensiveness in containing an unknown or undisclosed element but differs from it in that this is not the intrusion of irrational psychological factors but the uncertainty that exists as to what is really the matter and how serious it is. McDougall's Watchfulness and Freud's Signal-Anxiety are purely psychological concepts but they have an obvious connection with the biological and neurological concept of vigilance.
