Jim Young stood on a crate on the broad plaza outside the Department of Health and Human Services, a red megaphone in his right hand and, beneath his khaki shorts, an artificial left leg. "Limbs, limbs are not a luxury!" he chanted, leading nearly 150 people clustered around him who were wearing prostheses and matching orange T-shirts that said on the back, "Medicare amputees deserve legs too." Wednesday afternoon's modest protest was organized to attract outsize attention to concerns by the nation's amputees — and health practitioners who work with them — that the government might make it more difficult for older and disabled Americans to afford state-of-the-art artificial legs, or any artificial legs at all.