yeah, if you cut it deep, you definetly should go to the E.R.
I fell off my bike when a few weeks ago and my hand landed on some rocks out in the park...i didnt plan on going, but the park ranger insisted. I had to get 3 stitches

If its deep, definetly go. But if it is already 24 hours after the cut, they will have to put the glue (in most cases), if not they can probably stich it. Also, he would probably need a tetnis shot, and you cant buy them at the hardware store