This section is from the book "Materia Medica And Therapeutics Inorganic Substances", by Charles D. F. Phillips. Also available from Amazon: Materia medica and therapeutics.
In many non-parasitic forms of skin disease, mercurials are useful locally; sometimes by a "resolvent" action or quickening of the functions of the absorbents; sometimes by stimulating the epithelial and other tissues also; sometimes by exciting irritation of "substitutive character;" and in some cases by a powerful caustic effect. In syphilitic affections they exert a "specific" power, and in many cases their local action is supplemented by a varying amount of general action consequent on absorption. The late Mr. Startin, perhaps an empirical but certainly a successful practitioner in his specialty, and Mr. Naylor, who followed him, were accustomed to introduce mercury in some form into the treatment of almost all their cases; and if we do not use it so much, it is only that we have become more cautious than our predecessors as to doing harm by remedies.
M. Gubler has specially drawn attention to the cure sometimes obtained by mercurial treatment in very chronic skin-inflammation, such as psoriasis and eczema, and observes that it is a last resource not to be neglected, even if it be not easy to explain its action.