Some have conjectured that what in Arrian is named _laccos chromatinos_ was our indigo, which indeed might be classed among the lakes, according to the present meaning of that word. Others understand by it gum-lac[632]. But I am unacquainted with any proofs that gum-lac was known at so early a period. I much doubt whether this meaning of the word lac be so old; and I must confess that the opinion of Salmasius appears to me highly probable, namely, that Arrian alluded to a kind of party-coloured garment: for besides the grounds adduced by Salmasius, it deserves to be remarked, that in the passage in question different kinds of clothes, and no other articles are mentioned. Besides, the epithet _chromatinos_ is applied by the same writer, in the same sense, to other kinds of clothing. It cannot therefore be said that Arrian mentions our gum-lac, the origin of which word Salmasius endeavours to discover. In the works of Galen, which have not yet been sufficiently illustrated, I have found _Indicum nigrum_ only four times. In a place where he speaks of diseases of the eyes[633], he extols it on account of its cleansing quality; and says it can be used for wounds, when there is no inflammation. In another place[634], it occurs in three prescriptions for eye-salves. I have however endeavoured, but without success, to find in this excellent writer an explanation of what he calls _Indicum_; though he has explained almost all the different articles then used in the Materia medica. It appears therefore that the Greeks gave the name of _Indicum_ to our indigo, and also to Indian black or Indian ink. It however cannot be denied that, in opposition to this opinion, considerable doubts arise. Many who think that the black indigo (_nigrum Indicum_) of Pliny and Vitruvius was not ink, but our indigo, remark, that things of a dark blue or dark violet colour were by the Greeks and the Romans frequently named black; and therefore that the blue indigo might in this manner be called black[635]. But the examples adduced as proofs are epithets applied by the poets to dark-coloured flowers. Because nature produces no black flowers, the poets, who are fond of everything uncommon, extraordinary, and hyperbolic, call flowers black, when they are of so dark a tint as to approach nearly to black. Thus clear and deep water is called black. It is however hardly credible that painters and dyers, who must establish an accurate distinction between colours, should have spoken in so vague a manner. Salmasius suspects that _Nil_ and _Nir_, the Arabic names of indigo, have arisen from the Latin word _niger_.