PRINCETON – Forty years ago, I stood with a few other students in a busy Oxford street handing out leaflets protesting the use of battery cages to hold hens. Most of those who took the leaflets did not know that their eggs came from hens kept in cages so small that even one bird – the cages normally housed four – would be unable to fully stretch and flap her wings. The hens could never walk around freely, or lay eggs in a nest.