permutations in the molecules of the cells, and that the transmission from one nerve-cell to another of molecular vibrations and of chemical permutations gives us a mechanical explanation of the nervous life in animals and of the transmission of irritations in plants.
The result of all these researches is immense. Owing to them, we can now, without leaving the domain of purely physiological facts, understand how images and impressions are produced in our brain, and engraved on it; how they act upon one another, and how they give rise to conceptions and ideas. We can also understand the so-called "association of ideas"—that is, how new impressions revive the old ones.
An insight is thus gained into the very mechanism of thought.
We are certainly very far yet from knowing all that is to be known in this direction. Science only just now frees itself from the metaphysics which strangled it, and only scouts the borderland of this great domain. But a beginning has been made. A solid foundation has already been laid for further research. The ancient division into two separate domains, which the German philosopher Kant endeavoured to establish—the domain of phenomena which we examine "in time and space" (the domain of physics), and the other, which we are able to examine only "in time" (the mental phenomena)—this division has now to disappear, And to the question that was put one day by the materialist Russian physiologist, Professor Syetchenoff: "To which department does psychology belong, and who has to study it?" the answer has already been given: "It belongs to physiology, and it is the physiologist who has to study it, by the physiological method!" In fact, the recent researches of physiologists have already thrown infinitely more light on the mechanism of thought, on the origin of impressions, on their fixation in the memory and their transmission, than all the subtle discussions with which metaphysicians have entertained us for centuries.
Metaphysics is thus beaten now, in the stronghold itself which formerly belonged to it without contest. The domain of psychology, in which it formerly considered itself invincible, has also been invaded by natural sciences and by materialist philosophy, which has caused our knowledge in this branch to increase with a rapidity entirely unknown in former times.
However, among the works that appeared during these five or
