But it is precisely these metabolic phenomena that hold the key of life, and an organism in the course of evolution depends directly upon them. This problem concerns pedagogy in a very special way: when we have given food to the children in our schools, we have not yet completed our task of nourishing these children; for the phenomena of nutrition which take place in the hidden recesses of their tissues are very different from a simple intestinal transformation of aliments, and are influenced by the psychic conditions of the individual pupil.
Great workers not only need abundant nutriment, but they require at the same time a series of stimuli designed to produce "pleasure." The pleasures of life, necessary to human existence, include more than bread. In the history of social evolution there exist, side by side with the productions of labour, an entire series of enjoyments, more or less elevated, that constitute the stimului to production, and hence to evolution, and more profoundly still, to life itself.
The further man evolves and the more he produces, the more he ought to multiply and perfect his means of enjoyment.
Without stimuli, nutrition would grow less and less till it ended in death. Every-day experience in the punishment of criminals gives us proof of this. Confinement to a solitary cell is nothing else than a complete deprivation of psychic stimuli. The prisoner does not lack bread, nor air, nor shelter from the elements, nor sleep; his whole physiological life is provided for, in the strict material sense of the word. But the bare walls, the silence, the isolation from his fellow men in utter solitude, deprive the prisoner of every stimulus, visual, oral and moral.
The consequences are not merely a state of hopelessness, but a real and actual malnutrition leading to tuberculosis, to anemia, to death from atrophy. We may affirm that such a prisoner dies slowly of hunger due to defective assimilation; the solitary cell is the modern donjon, and far more cruel than the one in which Ugolino died within a few days, so much so that solitary confinement, being incompatible with life, is only of short duration.
Labour, love, and sensations apt to stimulate ideas, that is, to nourish the intelligence, are necessities of human life.
This is further proved by observations made regarding the development of puberty. Psychic stimuli may render such development precocious, and, on the contrary, their absence may retard it. Jean Jacques Rousseau relates in Émile that at Friuli he encountered young people of both sexes who were still undeveloped, although they were past the usual age and were strong and robust, and this he attributed to the fact that "owing to the simplicity of their customs, their imagination remained calm and tranquil for a longer time, causing the ferment in their blood to occur later, and consequently rendering their temperament less precocious."[27]
Recent statistical research confirms the intuitive observation of that great pedagogist; the women in the environs of Paris attain puberty nearly a year later than those who live in the city; and the same difference is observed between the country districts around Turin and those of the city itself.
All this goes to prove the fact of psychic influence upon physiological life: psychic excitation, experienced with pleasure, by developing healthy activities, aids the development of physical life.[28]
These principles must be taken under deep consideration when it comes to a question of directing the physiological growth of children. Fenelon relates a fable about a female bear who, having brought into the world an exceedingly ugly son, took the advice of a crow and licked and smoothed her cub so constantly that he finally became attractive and good-looking. This fable embodies the idea that maternal love may modify the body of the child, aiding its evolution toward a harmony of form by means of the first psychic stimuli of caresses and counsel.