The yellow fever, exercising its ravages upon shores equally distant from whites and negroes, has brought very decisive arguments into the question. We know, in fact, that the whites suffer in America from the black vomit in all its violence; whilst the Negroes are not attacked by it, or if they are, its effects are insignificant.[159] A ferocious maxim, one worthy of the conquerors, has explained--since the sixteenth century--this prerogative, which the Spaniards had so much reason to envy, “If we did not hang a Negro, he would never die.”[160] If some authors have timidly advanced the theory of a former acclimatisation[161] with regard to marsh-poisoning, the greater number of observers, Fenner, Nott, and Bryant, ought to admit that there was, even in the constitution of the black man, an obstacle--otherwise absolutely unknown in his nature--to the manifestation of the yellow fever;[162] and that the black blood appeared to carry on this resisting force to the mixed breed, even if they were born far away.[163] An extremely interesting experiment relating to this immunity of the Negro from the yellow fever, was tried largely during the disastrous Mexican expedition, and the conditions of this experience ought to give it a capital value. At first, our soldiers paid a terrible tribute to this scourge, and then the French Government took up the excellent idea of profiting by the resistance of the Negro race to the black vomit. It asked for a battalion of blacks from the viceroy of Egypt, consisting of men recruited from the limits of Soudan, from Berber to Khartoum. It was not without anxiety that the issue of this physiological experiment was watched, since it did not happen, as in our laboratories, _in anima vili_. Some had confidence in the functional uniformity of the Negro race, as being beyond all local action; others believing wrongly, as we said, in a former acclimatisation of the only inhabitants of the western coast of Africa, expected to find that all these Negroes from the other side of the continent would perish. However, in spite of what they had at first said, they could very soon verify the almost complete immunity of the Negro battalion at Vera-Cruz.[164] It was the first time, if we are not mistaken, that anthropology has been directly applied in the Old World to social science. Some time ago anthropologists were consulted by the government of the Northern States of America upon certain questions of slavery, at the time when terrible dissensions were budding in the shadows of the distance. CHAPTER V. INTELLECTUAL AND PHILOLOGICAL VARIETIES.