Upon these ideas there must now be grafted the concept of mutation and the observations of Hugo de Vries.--If this living substance which is common to all humanity should, at any time and owing to any influence, have acquired the capacity for changing[66] after a certain lapse of time, for instance a thousand years, then all those beings which have in them a share of this substance may suddenly undergo identical changes. It is well known that Hugo de Vries has observed such sudden variations in plants.[67] After centuries of stability in the characteristics of a species, quite suddenly, in a great number of individuals belonging to this species, there will one year occur a modification, the leaves becoming longer, or shorter, etc. Thenceforward this modification will be propagated as a constant feature, so that, by the following year, a new species will have come into existence.--The same thing happens among human beings, especially in the human brain; for, as far as man is concerned, the most striking instances of variation are found in the psychic domain. In each year, certain human beings present brain variations. Such abnormal individuals are sometimes regarded as madmen and sometimes as men of genius. They herald the coming variations of the species, variations of which they are the forerunners. At due date, the same peculiarities will suddenly manifest themselves throughout the species. Experience shows that transformations, or moral and social discoveries, appear at the same moment in the most widely separated and the most various countries. I have myself often been struck by this fact, both when studying history and when observing the men of my own day. Contemporary societies, at a great distance one from another and having no means of rapid intercommunication, will simultaneously exhibit the same moral and social phenomena. Hardly ever is a discovery born in the brain of a single inventor. At the same instant, other inventors happen upon it, anticipate it, or are hot upon the trail. The popular phrase runs, "the idea is in the air." When an idea is in the air, a mutation is about to occur in the human brain. We are, says Nicolai, on the eve of a "mutation of war." Moltke and Tolstoi represent the two great contrasted variations in human thought. Moltke extolled the ethical value of war; Tolstoi passed unqualified condemnation on war. Which of these two minds represents the variation of genius and which the variation of madness? In the light of contemporary events, most people would be inclined to give the palm to Moltke. But when an organism is about to undergo mutation, the change is often preluded by frequent and extensive variations. Of these divergent variations, those only persist which are best suited to the conditions of existence. Thus, in Nicolai's view, the ideas of Moltke and his disciples are a favourable presage that mutation is imminent. * * * * *