Gummas are lesions characteristic of the tertiary stage of syphilis.
These gummatous lesions can appear on the skin and on various organs as a reaction of tissues to invading bacteria. This occurs as a result of an infection that has been present for some time and that has not been properly treated, or not at all. For this reason, gummas are nowadays very rare in industrialised countries.
Here are some other gummas pictures:
Gumma of liver 2
Gumma of brain: 1 and 2