VOL. XLIII.] PHILOSOPHICAL TRANSACTIONS. 51 



forcibly driven into the capillary subcutaneous vessels, and shines through the epi- 

 dermis; but before, these vessels contained only a serous liquor, and accordingly 

 the skin appeared of that colour : which will further appear on squeezing such red 

 parts, which drives the blood out of them, and makes them appear white; whereas, 

 on removing such pressure, they recover their colour, as the blood does its place. 

 3. The yellow colour of the skin in the jaundice is a further proof of this assertion ; 

 where the yellow bile is diffused through the vessels of the cutis, and appears 

 through the epidermis ; but no one will imagine, that the epidermis itself receives 

 this viscid bile into its vessels ; which are so small, that many accurate anatomists, 

 as Morgagni, have denied it to have any vessels at all; and the most accurate 

 could never show them. 4. The pale look of those in whom the blood is viscid, 

 or circulates with little force, shows that the epidermis then transmits the colour 

 of the juices and fibres below it, which are then unmixed with red blood. 5. The 

 same is manifest in those whose blood is poor and serous, as the leucophleginatic, 

 &c. in whom the epidermis transmits the colour of the water or serum under it. 



Hence it appears, that the epidermis is a transparent membrane, which easily 

 shows the colour of the parts under it, in the same manner as the cornea of the 

 eye transmits the colour of the iris. And this will appear more plainly from some 

 considerations below; where we shall assign the cause of this pellucidity; and 

 show that the numbers of pores in the epidermis necessarily make it tranparent; 

 and that the smallness of the particles, into which it is divided by them, make it 

 unfit to reflect any rays of light, and consequently to manifest any colour of 

 its own. 



Prop. 2. — The Skins of Negroes are of a thicker Substance, and denser 

 Texture, than those of white People, and transmit no Colour through them. — For 

 the truth of the first part of this proposition, we need only appeal to our senses, 

 and examine the skins of negroes when separated from the body ; when not only 

 the cutis, but even the epidermis, will appear to be much thicker and tougher 

 than in white people. But because the substance and texture, especially of the 

 epidermis, is not a little altered in anatomical preparations, and that in such a 

 measure as to alter the texture perhaps, on which the colour depends, by boiling, 

 soaking, peeling, &c. let us examine the skins of negroes on their body ; where 

 they will appear, from the following considerations, to have all the properties 

 assigned : 1 . In bleeding, or otherwise cutting their skins, they feel more tough 

 and thick, than in white people. 1. When the epidermis is separated by can- 

 tharides, or fire, it is much tougher and thicker, and more difiicult to raise, in 

 black, than white people. 3. Negroes are never subject to be sun-burnt, or have 

 their skins blistered by any such degree of heat, as whites are. 4. Though their 

 skins, in some particular subjects, should not be so very thick in substance, yet 

 in winter, when they are dry, and not covered with that greasy sweat which 



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