One is the well-known case of Frederick Douglass, who, returning home after earnest service of weeks as Secretary of the Commission to report on the people of San Domingo and the expediency of incorporating them with the United States, was rudely excluded from the table, where his brother commissioners were already seated, on board the mail-steamer of the Potomac, just before reaching the President, whose commission he bore. This case, if not aggravated, is made conspicuous by peculiar circumstances. Mr. Douglass is a gentleman of unquestioned ability and character, remarkable as an orator, refined in manners, and personally agreeable. He was returning, charged with the mission of bringing under our institutions a considerable population of colored foreigners, whose prospective treatment among us was foreshadowed on board that mail-steamer. The Dominican Baez could not expect more than our fellow-citizen. And yet, with this mission, and with the personal recommendation he so justly enjoys, this returning Secretary could not be saved from outrage even in sight of the Executive Mansion. CASE OF LIEUTENANT-GOVERNOR DUNN. There also was Oscar James Dunn, late Lieutenant-Governor of Louisiana. It was my privilege to open the door of the Senate Chamber and introduce him upon this floor. Then, in reply to my inquiry, he recounted the hardships to which he had been exposed in the long journey from Louisiana,--especially how he was denied the ordinary accommodations for comfort and repose supplied to those of another skin. This denial is memorable, not only from the rank, but the character of the victim. Of blameless life, he was an example of integrity. He was poor, but could not be bought or bribed. Duty with him was more than riches. A fortune was offered for his signature; but he spurned the temptation. And yet this model character, high in the confidence of his fellow-citizens, and in the full enjoyment of political power, was doomed to suffer the blasting influence which still finds support in this Chamber. He is dead at last, and buried with official pomp. The people, counted by tens of thousands, thronged the streets while his obsequies proceeded. An odious discrimination was for the time suspended. In life rejected by the conductor of a railway because of his skin, he was borne to his last resting-place with all the honors an afflicted community could bestow. Only in his coffin was the ban of color lifted, and the dead statesman admitted to that equality which is the right of all. REQUIREMENT OF REPUBLICAN INSTITUTIONS.