The Republic by Plato Part 2 Page 57

And the selection will be no easy matter, I said; but we must be brave and do our best.

We must.

Is not the noble youth very like a well-bred dog in respect of guarding and watching?

What do you mean?

I mean that both of them ought to be quick to see, and swift to overtake the enemy when they see him; and strong too if, when they have caught him, they have to fight with him.

All these qualities, he replied, will certainly be required by them.

Well, and your guardian must be brave if he is to fight well?

Certainly.

And is he likely to be brave who has no spirit, whether horse or dog or any other animal?