The unanimous decision of the U. S. Supreme Court 50 years ago that separate schools for blacks and whites were unconstitutional did not at first raise the consciousness of the generation of white Southern children who were just coming of age. Discrimination was just a word and not many knew of its rawer and common aspects, which took the form of humiliation, brutality and even murder. Having no interest though living in its midst, we had familiarity but little knowledge. In a few months, Emmett Till would change that. Till, a 14-year-old Chicago lad who was visiting his great aunt and uncle in a sharecropper cabin near Money, Miss., had the effrontery to whistle at a white woman on a dare from other children. For that, he was taken from the cabin in the night, bound in barbed wire, tortured and shot. His horribly mutilated body, tethered to a 75-pound cotton-gin fan, was thrown in the Tallahatchie River. While the country was marking the 50th anniversary of Brown v. Board of Education the Justice Department last week said it was reopening the investigation of Till's kidnapping and murder, which went unpunished in Mississippi. Not that there was ever any doubt about who killed him. J. W. Milam and his brother-in-law Roy Bryant bragged about it and were local heroes. There is the question of what the government can possibly hope to achieve since Milam and Bryant are dead and there seems to be no adequate way to administer justice in such a case. Our annals are full of such unrequited crimes against blacks, including the massacre 85 years ago of hundreds of men, women and children in Phillips County, Ark., whose only offense was being black and defenseless. But the country might be in a mood to pay attention, even if it cannot exact justice. This is a thin substitute but worthwhile. Good citizens, apparently from President Bush on down if you trust his words, are wondering how genuine Americans could humiliate, torture and murder Muslims who had fallen into U.S. custody. We are assured officially that only a handful of low-ranking soldiers did it, unbeknownst to higher-ups, although the inhumanity seems to have been common and to have followed directives from the top. Even the self-analysis is not universal. The instant surveys show that many think that it was not so bad, that we had good reason and that, anyway, it was traitorous to reveal it, especially to show pictures. What a generation learned first from Emmett Till, a boy so obscure that his murderers didn't even bother to learn his name, is that you can dehumanize a class of people, whether it be by race, religion or sexual proclivity, so that human rights do not settle on them. We can bear to sit for that lesson again. Emmett Till ignited the civil rights movement and for that we owe a sharecropper named Mose Wright, whose name never appears in the pantheon of civil rights heroes. When Milam and Bryant showed up at his cabin and hustled his nephew away, Wright put his hysterical wife on the bus for Chicago and went into town to tell the sheriff what had happened. They found Till's battered body and shipped it to Chicago, where his mother insisted on an open coffin for the funeral so that the world could see what had been done to her boy. John Henry Johnson, a slave descendant who grew up across the Mississippi River at Arkansas City, Ark., ran the gruesome picture in his new magazine Jet and started a firestorm. No four-star general called to advise him to hold off for the good of the country. Owing to Mose Wright, they had to arrest Milam and Bryant and the country was treated to the spectacle of the state of Mississippi for the first time trying white men for the murder of a black. The AP gave us an antiseptic account of the trial. A young Arkansan could go to his college library and read a better one from Murray Kempton, the finest columnist who ever lived, in the pages of the New York Post. Kempton's unforgettable lede: "Mose Wright, making a formation no white man in his county really believed he would dare to make, stood on his tiptoes to the full limit of his 64 years and his 5 feet 3 inches yesterday, pointed his black, workworn finger straight at the huge and stormy head of J. W. Milam and swore that this was the man who dragged 14-year-old Emmett Louis Till out of his cottonfield cabin the night the boy was murdered. "'There he is,' said Mose Wright. He was a black pigmy standing up to a white ox. J. W. Milam leaned forward, crooking a cigarette in a hand that seemed as large as Mose Wright's whole chest, and his eyes were coals of hatred." "Mose Wright took all their blast straight in his face, and then, for good measure, turned and pointed that still unshaking finger at Roy Bryant, the man he says joined Milam on the night-ride to seize young Till for the crime of whistling suggestively at Bryant's wife . . .'And there he is, Mr. Bryant.' " An all-white jury happily acquitted them and Milam shortly gave an interview in which he said they killed the boy to send a message. Even the sterile accounts etched in our collective consciousness what had been done in our name. We seem never to have advanced so far that we cannot profit from such reminders.