We owe a very good observation to Camper: “The black colour which is noticed in the natural parts of both sexes, and even in white individuals, clearly proves that our reticular membrane has its colour only from the blood.”[222] This fact alone should have long ago given a more rational impulse to researches on this subject. If--putting all these hypotheses on one side, for all that we can bring forward has no other value--if we wish to study in a _positive_ manner the influence of the sky upon man, we have only in reality one resource,--it is to shut ourselves up in the limits of history, to study the effect of the migrations of which it tells us, and to see whether man, transported far away, _does_ become modified, and how this modification takes place. Then we shall find two answers to these questions, which form together a kind of anthropological law. LAW.--_In historical times, either man_ (we mean a society of men) _who is taken far from his medium does not alter his type, or he entirely disappears_. What nation has been transformed? We cannot answer, even with history in our hand; we know not of any. And yet, the short period of time embraced by the records of mankind would be quite sufficient if it were true, as Isidore Geoffroy thought, that we could conclude from animals to men, and that two thousand years would have been sufficient to alter fundamentally the _genus_ stag.[223] It is a well-known fact, that the inhabitants of the Island of Bourbon, who were colonists established in the high lands for two centuries, have preserved intact the purity of their blood.[224] The Spanish and Portuguese families established in Brazil, and who have carefully avoided foreign marriages, have lost nothing, it is said, of their original characteristics.[225] The Icelanders have not become Laplanders in their own island, and they have now been established there eight hundred years; they are as fair and _German-looking_ as at first.[226] The Dutch have prospered at the Cape under the name of Boers. They say that at Cochin and Malabar there exists a Jewish tribe, which has been established there for a long time, and which traces back its origin to the captivity; it has remained pure,[227] and as similar to the inhabitants of the Jewish quarter at Cairo, as to the Jews in Leonardo da Vinci’s Last Supper, and in the pictures of the Flemish school.