Reflexes are considered mostly as purely mechanical actions. It is supposed that from an entirely physicochemical point of view one can understand them more easily than one can actions of will or of purpose. In his classic book on the "Integrative Action of the Nervous System," Sherrington, however, emphasized not only that the simple reflex is a purely abstract conception, but that the reflex also is an action the initiation of which is traceable to events in the environment, and he began his analysis of reflexes with an instance which every one would consider a real action: An animal turns its head in response to sudden illumination. He added that in the light of the darwinian theory, every reflex must be purposive and that the effect of every reflex is to enable the organism in some particular respect better to dominate the environment. Sherrington took the reflex as the unit