3. Kant, Blumenbach, and Humboldt, offer different modifications of a chemical hypothesis, to account for the dark colour of the rote mucosum. The first of these authors supposes that the blood of negroes abounds in iron, which is precipitated into this membrane by the phosphoric acid. Blumenbach is of opinion, that the carbon which abounds in the body is thrown off by the cud., vera, united with hydrogen, hut is decomposed by the access of the oxygen of the atmosphere, IA bile the carbon remains fixed in the rote nzueosum; and Hum boldt ascribes the .dark complexion of the Indians of South A nerica to the abundant deposition of carburet ted hydrogen in the corpus mucosum, or retie:datum of Malpighi ; this, he supposes, not only is the proxi mate cause of darkness of complexion, but also of the fact, that those races in which it exists retain their na Live colour, even under the influence of a colder cli mate.
4. The remaining class of hypotheses rests on a diffe rent foundation. Blumenbach, besides giving it as his opinion that the proximate cause of the dark colour of the rote mucosum is the abundance of carbon which re mains fixed in that membrane, endeavours to account for the secretion of this substance in such quantity. I lot climates, he says, exert a great influence on tor li ver: an unnatural state of the bilious secretion being thus produced, and increased through many genera tions, the vessels of the skin secrete a greater abun dance of carbon than in colder climates. But this hypo thesis is extremely weak and ill-founded ; besides in volving the idea that the negro race are constantly la bouring under hepatic disease, it is directly contradicted by the fact, " that bile has no power in producing a per manent change in the colour of the skin ; and sickness, which in hot climates causes the skins of Europeans to assume a yellow hue, changes that of the African to a lighter colour." Winterbottom, vol. i. p. 190.
Dr Rush has advanced an hypothesis of a similar na ture to that just noticed, but still more weak and liable to objections ;—he supposes that leprosy is the cause of the black complexion and woolly hair of the negrocs: It will be sufficient to state two of his arguments to prove how hard he is pushed to support this opinion, and how very absurdly, after all, he does support it : leprosy is accompanied, in some instances, with a black colour of the skin, therefore the black complexion of the negroes arises from this cause ; but leprosy is also described as giving rise to preternatural whiteness ; hence this disease may also be considered as the cause of the singular complexion of the Albinos, or white ne groes. His mode of accounting for the woolly hair of the Africans on this hypothesis is equally unphilosophi cal : some medical writers look upon the Mica poionica as a species of leprosy, but the hair in the Mica poionica bears some slight resemblance to the hair of negroes, therefore the leprosy is the cause of two of the most distinguishing characters of this race, the blackness of their complexion and the crispature of their hair. This
kind of reasoning is not unworthy of the man, who, in the same paper, could express his belief, that two women bad became black, and got the features of negroes, by living with negro husbands. This, too, is an additional proof, that all negroes arc lepers, as it puts it beyond a doubt that they are infectious. See dimeriean Transac tions, vol. iv. p. 289, Scc.
The different varieties of human complexion have been classed by several authors : the classification of Blumenbach, with some little alteration, is the most clear, methodical, and satisfactory. We shall give his classification of the more striking features, as well as of complexion, because, from the union and concomitan cy of particular sets of features, with particular kinds of complexion, an argument will afterwards be drawn respecting the influence of climate on the human com plexion.
According to this author, there are five varieties ; the Caucasian, the the Malay, the Ethiopian, and the American.
I. In the Caucasian variety, the skin is white, or rather brownish ; the cheeks are red, and the hair of the different shades, from black to y ellow, or red. The form of the head is nearly globular ; the face oval and straight ; the forehead expanded ; the nose narrow at the base, and rather aquiline ; the mouth small ; the lower lip a little turned out, and the chin full and rounded. In this variety, Blumenbach includes all the Europeans except the Laplanders, the western Asiatics, including the Georgians, Caucasians, Persians, Arabi ans, &c. the northern Africans, and the Abyssinians. At first, he was disposed to arrange the Egyptians in this variety, but afterwards he altered his opinion, and placed them between the Circassian and Ethiopian. Observations on some Egyptian Mummies, by J. F. BM menbach, in the Philosophical Transactions for 1794. The Gothic or German race has also been taken out of the Caucasian variety by Dr Pritchard, and formed into a separate class, under the name of " Constitutia Germanica ant Sanguinea." (Disputatio inauguralis de hominum varietatibus. Auct. J. C. Pritchard.) This has been done, rather on account of their difference in complexion than in features. They are characterized by blue eyes, flaxen hair, and very fair skin ; their fea tures are more rounded, and their eyes smaller than those of the nations which form the Caucasian variety. The Danes, Norwegians, and Icelanders, exhibit the pe culiar features and complexion of the Gothic race, in their purest state.