A very common phenomenon, and one very familiar to the student of history, is this. The customs, beliefs, or needs of a primitive time establish a rule or a formula. In the course of centuries the custom, belief, or necessity disappears, but the rule remains. The reason which gave rise to the rule has been forgotten, and ingenious minds set themselves to inquire how it is to be accounted for. Some ground of policy is thought of, which seems to explain it and to reconcile it with the present state of things; and then the rule adapts itself to the new reasons which have been found for it, and enters on a new career. The old form receives a new content, and in time even the form modifies itself to fit the meaning which it has received. The subject under consideration illustrates this course of events very clearly. I will begin by taking a medley of examples embodying as many distinct rules, each with its plausible and seemingly sufficient ground of policy to explain it. [6] A man has an animal of known ferocious habits, which escapes and does his neighbor damage. He can prove that the animal escaped through no negligence of his, but still he is held liable. Why? It is, says the analytical jurist, because, although he was not negligent at the moment of escape, he was guilty of remote heedlessness, or negligence, or fault, in having such a creature at all. And one by whose fault damage is done ought to pay for it. A baker's man, while driving his master's cart to deliver hot rolls of a morning, runs another man down. The master has to pay for it. And when he has asked why he should have to pay for the wrongful act of an independent and responsible being, he has been answered from the time of Ulpian to that of Austin, that it is because he was to blame for employing an improper person. If he answers, that he used the greatest possible care in choosing his driver, he is told that that is no excuse; and then perhaps the reason is shifted, and it is said that there ought to be a remedy against some one who can pay the damages, or that such wrongful acts as by ordinary human laws are likely to happen in the course of the service are imputable to the service. Next, take a case where a limit has been set to liability which had previously been unlimited. In 1851, Congress passed a law, which is still in force, and by which the owners of ships in all the more common cases of maritime loss can surrender the vessel and her freight then pending to the losers; and it is provided that, thereupon, further proceedings against the owners shall cease. The legislators to whom we owe this act argued that, if a merchant embark a portion of his property upon a hazardous venture, it is reasonable that his stake should be confined to what [7] he puts at risk,--a principle similar to that on which corporations have been so largely created in America during the last fifty years.