What are these bricks with filled interior and holes/tubes going through? I recently bought at haul and found a bunch of these regular sized bricks. Can anyone identify the for me?

They are 2x4 bricks, but with holes in the side of the bricks:


From: http://imgur.com/a/hOGto

It says Lego on the stud, but no part numbers are to be found anywhere, so I guess they are old.

Any help is appreciated.
They were used until 1990 for trains, the holes are there to stick in the wheels.

This is the part: http://www.bricklink.com/catalogItem.asp?P=7049b
And these (for example) were the wheels: http://www.bricklink.com/catalogItem.asp?P=wheel2a