Sentence:  ... it must be observed that both vegetable and animal substances become bleached white by the sun-beams when they are dead, as cabbage-stalks, bones, ivory, tallow, bees-wax, linen and cotton cloth; and hence I suppose the copper-coloured natives of sunny countries might become <WSD>etiolated</WSD> or blanched by being kept from their infancy in the dark, or removed for a few generations to more northerly climates. 
Meaning of the word marked with <WSD> tags:  Blanched because of sunlight deprivation or excessive exposure to sunlight.