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Proof in fome Negroes labouring under a bilious Fever, 
in whom the Serum of the Blood, when let, was of a 
deep bilious Yellow, but no yellow Colour appeared 
on the Skin, altho’ plain enough to be feen in the 
Eyes, 
Corollary . From hence might be deduced one plain 
Caufe of the Blacknefs of Negroes j for, if the Colour 
of the Skin depends on what it tranfmits, and the 
Skins of Negroes tranfmit no Colour thro 1 them, they 
mud, for that Reafon, appear black 5 according to 
the known Dodrine of Light and Colours, Thar, 
where-ever there is a Privation of Light or Colour, 
there, of courfe, enfues Darknefs or Blacknefs. But, 
as moft folid Bodies, which are not pellucid, do 
generally refled fome Colour, which we know no 
black Body does, we fhall next inquire into the par- 
ticular Make of their Skins, by which they are ren- 
dered incapable to refled, as well as to tranfmit, the 
Rays of Light. 
Proposition III, 
The Part of the Skin which appears black in Ne- 
groes , is the Corpus reticulare Cutis, and external 
Lamella of the Epidermis : And all other Parts 
are of the fame Colour in Them with thofe of 
white People , except the Fibres which pafs be- 
tween thofe Two Parts . 
For a Proof of this Propofition, we muft examine 
the Strudure of the Skins of Negroes more narrowly, 
which may be done after Bliftering with Cantharides , 
or after a Scald or Burn 5 when their Skins have 
appeared to me in the following Manner : The Cuti- 
cle, 
