a legal scholar once quipped that the limits to prison population are not absolute, but "like the elastic on underwear: slightly more uncomfortable with each expansion." That assessment, made when America housed 60 percent fewer prisoners, now seems optimistic. In 2006, federal prisons were 37 percent over capacity while some state systems bulged with more than double their intended numbers. Packing in too many inmates can spread disease and spur violence and suicide. The dangers are hardly a new revelation. One of the main gripes of inmates who rioted at Attica in 1971, leaving 43 people dead: The prison was 40 percent overbooked.