ABSTRACT
In the simplest known organisms that have not evolved in the vegetal direction, we find positive or negative reactions in face of external excitations, and it might be supposed that if these excitations suited the interest of the living being, this would be the chance outcome of repeated selection. But we find an aptitude for profiting by experience, the formation, for example, of a negative reaction in the presence of nocuous stimuli, just as if the production of a disagreeable affective impression had involved the reversal of an initial reflex attitude.
