And finally the Romans themselves, in spite of their sanitary measures, became from year to year more alien in blood from the genuine stock of Romulus and Remus, until the distinctive characters of the conquerors of the earth finally disappeared. The Latins, Sabines, and primitive Etruscans pressed constantly upon them with the irresistible force of destiny. When Scipio Æmilianus was interrupted in the forum by this mongrel populace, he exclaimed, "Silence, false sons of Italy! Think ye to scare me with your brandished hands, ye whom I led myself in bonds to Rome?" When the fierce and hardy Northmen descended into Southern Europe, they carried along with their laws a chastity and a reserve that excited universal surprise. But these virtues were not of long continuance there; the climate and the customs of the new society soon warmed their frozen imaginations, and their laws by degrees relaxed, and their manners even more than their laws. The giants of the North many times swept down over the plains of Italy, and regenerated with fresh and pure blood the puny breeds of degenerate Rome, but they have since disappeared, and their descendants are no longer to be found in these countries. VII. In relation to the futile efforts of Spain in Mexico, the ethnologist Knox exclaims, "Neither climate, nor government, nor external influences ever alter race. They may and they do affect them, and in time destroy them, but they never give rise to a new race. In half a century the dreams of Humboldt, of Canning, of Guizot, and other profound statesmen, have come to a close, and Nature once more, as I long ago predicted, asserts her rights." Naturalists, from Hippocrates to Buffon, have believed that climate, heat and cold, dryness and humidity, the qualities and abundance of nourishment, have power to modify men and animals, but "neither climate, nor government, nor external circumstances ever give rise to a new race." The generous qualities once gone, are departed forever, and their loss can rarely be retrieved. Where is the instance of a fallen man, class, or nation? "The history of nations," writes the Registrar-General of England,--"the history of nations on the Mediterranean or the plains of the Euphrates and Tigris, the deltas of the Indies and Ganges, and the rivers of China, exhibits the great fact: the gradual descent of race from the highlands, their establishment on the coasts, in cities sustained and refreshed for a season by emigration from the interior--their degradation in successive generations under the influence of the unhealthy earth, and their final ruin, effacement, or subjugation by new races of conquerors. The causes that destroy individual men lay cities waste, which, in their nature, are immortal, and silently undermine eternal empires.