Eliza is still crossing the ice. The spectacle (in the form of a series of waves of chemical decomposition) is on its way, through reflex arcs, to striped and unstriped muscles; to ductless glands; to effectors, in short. It is time that some action ensued, that behavior on Eliza’s part resulted in behavior on the part of the spectator. Let us suppose that the spectator most interested is a bloodhound. “The behaviorist,” we learn from Dr. Watson[9] “recognizes no dividing line between man and brute,” save (he adds later) perhaps in the matter of “language.” As the occasion here affords no time for talk, a bloodhound will serve as well as Senator Borah. Now what will the bloodhound do? Were his reflexes unconditioned, he would do nothing of any consequence. On the unlikely chance of Eliza throwing a stone and hitting him on the patellar tendon, he might do a knee-jerk. Or, should her shadow come between him and the sun, the iris of his fearful eyes might contract. But none of these things happen. Eliza furnishes no natural stimuli upon which an unconditioned reflex could act. Prof. Loeb, with all his tropisms, would be able to bring no real drama about. This is a Watson bloodhound, however--a trained dog. All sorts of unnatural stimuli have been grafted upon his reflexes. For one thing, he has had the sight of little girl and the taste of little girl brought simultaneously into his experience a great many times. So the glands in his cheeks advance immediately from a salivary output of, say, five drops per minute, to some forty-five. He probably snaps his jaws, a “seeking motion” prompted by the emotion of love--for meat. Not only that, but he bounds forward--another seeking motion, which was once, I presume a puppy squirm. Anyway he bounds forward, and Eliza is caught. Or else he does not bound forward, but stands and sniffs, whines, or gives tongue, thus bridging the space between animal and man, but flatly refusing to attempt to leap the space of open water between dog and Eliza’s cake of ice. But why? Why does not the dog act automatically in obedience to the waves of chemical decomposition faithfully transmitted to his effectors? The villain of uncertainty lies in that intermediate set of neurones--those association neurones which Dr. Watson thinks have received already altogether too much attention. Some of their dendrites have made synapse with axones laden with the fear of the cold wetness of ice-water, and have communicated, not with the leaping but with the sniffing, whining and baying muscles, leaving the legs merely trembling.