ABSTRACT
This chapter discusses the evolution of sensibility, from the most elementary phases under which it shows itself at its point of origin, to the moment of its most complete expansion in man. Sensibility is that fundamental property which characterizes the life of cells. Attraction for agreeable and repulsion for disagreeable things are the indispensable corollaries of every organism fitted for life, and apparently the elementary manifestation of all sensibility. In vegetables the phenomena of sensibility have already taken more distinctly marked forms. The phenomena of sensation in the superior animals are, then, simple phenomena, constituted by the mere reaction of a tissue in the presence of external excitations; they are the complex subordinated operations of the nervous activity which require the participation of a great many organs successively brought into play, in a order to arrive at the complete evolution.
