The possibility of observing the developments of the psychical life of the child as natural phenomena and experimental reactions transforms the _school itself in action_ into a kind of scientific laboratory for the psycho-genetic study of man. It will become--perhaps in the near future--the experimental field _par excellence_ of the psychologist. To prepare such a school as perfectly as possible, is therefore not only to prepare "a better method for the education of children," but also to prepare the materials for a renovated science. Every one now knows that students of natural science require in their laboratories an organization directed to the _preparation_ of the material to be observed. To observe a simple cell in movement, it is necessary to have a hollow glass slide with cavity for the hanging drop; to have ready "fresh solutions" in which the living cells may be immersed, to ensure their continued vitality; to have ready soils for cultures, etc. For all these ends there are special avocations, those of the so-called "preparers," who are not the assistants or helpers of the professor, but _employes_ who were at one time upper servants, and then become superior workmen. At the present day they are, however, nearly always themselves scientific graduates. For, indeed, their task is a most delicate one; they must possess biological, physical, and chemical knowledge, and the more thoroughly they are "prepared" by a culture analogous to that of the masters of research themselves, the more rapid and secure is the march of science. It is strange to think that among all these laboratories of natural science, only that of "experimental psychology" has judged it possible to dispense with an organization for the preparation of the subjects to be observed. If to-day a psychologist were told to arrange the work of his preparer, he would take this to mean the preparation of his "instruments," thus adopting more or less the standard of laboratories of _physics_. But the idea of preparing the living being which produces the phenomenon would not enter his mind; and yet, if merely to observe a cell, a living microbe, the scientist needs a "preparer," how much greater must be the necessity for such an assistant when the subject to be observed is man! Psychologists consider that they can prepare their "subjects" by arresting their attention with a word, and explaining to them how they are to proceed in order to respond to the experiment; any unknown person met by chance in the laboratory will serve their purpose. In short, the psychologist of to-day behaves somewhat like the child who catches a butterfly in flight, observes it for a second and then lets it fly away again; not like the biologist who takes care that his preparations are properly carried out in a scientific laboratory.