It would be for us now to speak of the physiological characteristics of the human race; but our consideration of this subject will be limited to a few words, since the condition of physiological functions is almost identical among all men, whatever be their race.
There is, nevertheless, an important difference, well worthy of note, presented by the nervous system when we compare the two extremes of humanity, namely, the Negro and the white European. In the white man, the nervous centres, that is the brain and spinal cord, are of much greater volume than they are in the Negro. In the latter the expansions from these nervous centres, that is, the nerves properly so called, have relatively a greater volume.
A similar difference, quite on a par with this, exists in the circulatory system. In the white man, the arterial system is more developed than the venous; the reverse is the case with the Negro. Lastly, the blood of the Negro is more viscous, and of a deeper red than that of the white man.
With the exception of these general differences, the great physiological functions proceed in the same manner among all races of men. The differences are not remarked except when secondary functions are compared, but these differences then assume proportions of some consideration.
Climate, customs, and habits are the causes of these variations in the secondary functions, which at times become so similar as to permit of confusion in the most opposite races. Let a member of the white race be thrown into the midst of wild Indians, become a prisoner of the red-skins, and share their warlike existence in the midst of forests, we shall see that the sense of sight, as also that of hearing, will attain in this individual the same perfection which they enjoy in his new companions. It is by virtue of the prodigious flexibility of our organism, and of our powers of imitation and assimilation, that the physiological functions of secondary importance become capable of such modification.
The intellectual and moral characteristics are those which take the lead in man. Not only are we unable to pass them over in silence in the general study of the human race, but much more importance must be assigned to them than to mere corporeal characteristics. If the naturalist, when he studies an animal, makes a point, when he has described his structure and organism, of considering his habits and manner of life, how much more should he, when treating of man, dwell upon his intellectual faculties, the stamp which so truly identifies our species.