Page:Popular Science Monthly Volume 2.djvu/571

Rh IV. —The study of diseases presents entirely similar facts, and conducts to the same conclusions.

All the human races are accessible to the same diseases. If any circumstances—isolation, for instance—have preserved some one of them from affections common to the others, a simple coming together suffices for the propagation of the disease. The eruptive maladies seem to have been implanted in America by the Europeans; but, once implanted among the indigenous races, they have raged with—a violence that we know not a violence which is accounted for by the kind of life led by these people.

Yet immunities, at least relative, have been proved. For instance, the negro race is much less sensible to the emanations of marshes, to the miasms from stagnant waters, than the white race. In return, it is much more easily affected by phthisis.

Other more complete immunities have been observed, and some have even wished, in consequence, to justify the admission of a distinct human species. But these immunities, even the best marked, disappear with time, and still more under the influence of conditions of existence. I will give you a curious example:

Elephantiasis is a hideous malady, peculiar to certain warm countries, which swells and deforms, sometimes in the strangest way, the parts of the body it attacks. In one of the Antilles, in Barbadoes, this disease was seen from the first among the negroes, but had constantly spared the whites, till 1704. That year a white person was seized, and since then the malady has extended in this race; but it never attacks any but Creoles. Up to the present time, Europeans, who settle in this isle, enjoy the ancient immunity. You see it is only a question of complete acclimation.

Gentlemen, I believe I have sketched, in this one lecture, a body of facts and ideas which, at the museum, occupied at least ten lectures, each as long as this to-day. So, you see how many things I have been compelled to omit. Incomplete as I have been compelled to make this presentation, it is sufficient, I think, to establish clearly some general facts, and prepares the way for an important conclusion.

You have seen that, considering man from the point of view of his height and color, we may form a graduated series which passes from one extreme to the other by insensible shades. You have seen further that, in this series, groups the most distinct by other characters—the most separated by their habitat—are found intermixed.

Permit me to add that we should get the same result, whatever the exterior or anatomical character upon which we establish our series.

The study of functions, whether performed in a normal manner, in a state of health, or under the perturbing influence of disease, shows us identical fundamental facts revealing the unity of human nature.

Even apparent exceptions come under the general facts when we