Several kinds of pediculus, the itch insect (acarus scabiei), and without doubt other acari also, occur both in and upon the skin: the subcutaneous cellular tissue is infested with the filaria medi-nensis already alluded to (p. 22).

Among vegetable productions may be mentioned the thread fungi (fadenpilze), which are formed in the pustules in cases of porrigo favosa. They are the primary anomaly, and constitute unquestionably the essence of the whole disease.