Every one is familiar with Bacon's famous passage about the dog, and the noble courage which that animal puts on when "maintained by a man; who is to him in place of a God, or _melior natura;_ which courage is manifestly such as that creature, without the confidence of a better nature than its own, could never attain." Not so. The dog is a social animal, and acts instinctively in concert with his fellows; and the courage he manifests is of the family, not the individual. In the domestic state the man he is accustomed to associate with and obey stands to him in the place of the controlling pack, and to his mind, which is canine and not human, _is_ the pack. A similar "noble courage," greatly surpassing that exhibited on all other occasions, is displayed by an infinite number of mammals and birds of gregarious habits, when repelling the attacks of some powerful and dangerous enemy, or when they rush to the rescue of one of their captive fellows. Concerning this rage and desperate courage of social animals in the face of an enemy, we see (1) that it is excited by the distressed cries, or by the sight of a member of the herd or family dying from or struggling in the clutches of an enemy; (2) that it affects animals when a number af individuals are together, and is eminently contagious, like fear, that communicates itself, quick as lightning, from one to another until all are in a panic, and like the joyous emotion that impels the members of a herd or flock to rush simultaneously into play. Now, it is a pretty familiar fact that animals acting instinctively, as well as men acting intelligently, have at times their delusions and their illusions, and see things falsely, and are moved to action by a false stimulus to their own disadvantage. When the individuals of a herd or family are excited to a sudden deadly rage by the distressed cries of one of their fellows, or by the sight of its bleeding wounds and the smell of its blood, or when they see it frantically struggling on the ground, or in the cleft of a tree or rock, as if in the clutches of a powerful enemy, they do not turn on it to kill but to rescue it. In whatever way the rescuing instinct may have risen, whether simply through natural selection or, as is more probable, through an intelligent habit becoming fixed and hereditary, its effectiveness depends altogether on the emotion of overmastering rage excited in the animal--rage against a tangible visible enemy, or invisible, and excited by the cries or struggles of a suffering companion; clearly, then, it could not provide against the occasional rare accidents that animals meet with, which causes them to act precisely in the way they do when seized or struck down by an enemy. An illusion is the result of the emotion similar to the illusion produced by vivid expectation in ourselves, which has caused many a man to see in a friend and companion the adversary he looked to see, and to slay him in his false-seeing anger.