The occurrence of war between nations renders obvious certain manifestations of the social instinct which are apt to escape notice at other times. So marked is this that a certain faint interest in the biology of gregariousness has been aroused during the present war, and has led to some speculation but no very radical examination of the facts or explanation of their meaning. Expression, of course, has been found for the usual view that primitive instincts normally vestigial or dormant are aroused into activity by the stress of war, and that there is a process of rejuvenation of “lower” instincts at the expense of “higher.” All such views, apart {140} from their theoretical unsoundness, are uninteresting because they are of no practical value. It will be convenient to mention some of the more obvious psychological phenomena of a state of war before dealing with the underlying instinctive processes which produce them. The war that began in August 1914 was of a kind peculiarly suitable to produce the most marked and typical psychological effects. It had long been foreseen as no more than a mere possibility of immense disaster—of disaster so outrageous that by that very fact it had come to be regarded with a passionate incredulity. It had loomed before the people, at any rate of England, as an event almost equivalent to the ultimate overthrow of all things. It had been led up to by years of doubt and anxiety, sometimes rising to apprehension, sometimes lapsing into unbelief, and culminating in an agonized period of suspense, while the avalanche tottered and muttered on its base before the final and still incredible catastrophe. Such were the circumstances which no doubt led to the actual outbreak producing a remarkable series of typical psychological reactions. * * * * *