Sentence:  "On the Poison of Serpents." By W. Boag, Esq. [...] Supposing the fatal effect [of a snakebite] to be produced by the sudden subtraction of oxygen from the blood, this gentleman recommends, by way of antidote, the employment of those substances which contain oxygen in its greatest abundance, and part with it with the greatest facility; and, as <WSD>lunar</WSD> caustic &#91;silver nitrate&#93; possesses these properties in a singular degree, he concludes that no medicine is better calculated to resist the effects of the poison of serpents. 
Meaning of the word marked with <WSD> tags:  Of or pertaining to silver (which was symbolically associated with the Moon by alchemists).