The Collaborative International Dictionary of English v.0.48:

Dartrous \Dar"trous\, a. [F. dartreux. See Dartars.] (Med.)
   Relating to, or partaking of the nature of, the disease
   called tetter; herpetic.
   [1913 Webster]

   Dartrous diathesis, A morbid condition of the system
      predisposing to the development of certain skin diseases,
      such as eczema, psoriasis, and pityriasis. Also called
      rheumic diathesis, and herpetism. --Piffard.
      [1913 Webster]