interesting to trace the transformation throughout its whole
extent, but the story will also afford an instructive example of
the mode in which the law has grown, without a break, from
barbarism to civilization. Furthermore, it will throw much light
upon some important and peculiar doctrines which cannot be
returned to later.

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