Macduff. What's the disease he means?

Malcolm. 'Tis called the evil:

A most miraculous work in this good king;

Which often, since my here-remain in England,

I have seen him do. How he solicits heaven,

Himself best knows: but strangely visited people,

All swoln and ulcerous, pitiful to the eye,

The mere despair of surgery, he cures,

Hanging a golden stamp about their necks,

Put on with holy prayers: and 'tis spoken,